diff --git a/vendor/golang.org/x/text/language/parse.go b/vendor/golang.org/x/text/language/parse.go
index fca2d30..11acfd8 100644
--- a/vendor/golang.org/x/text/language/parse.go
+++ b/vendor/golang.org/x/text/language/parse.go
@@ -5,216 +5,21 @@
 package language
 
 import (
-	"bytes"
 	"errors"
-	"fmt"
-	"sort"
 	"strconv"
 	"strings"
 
-	"golang.org/x/text/internal/tag"
+	"golang.org/x/text/internal/language"
 )
 
-// isAlpha returns true if the byte is not a digit.
-// b must be an ASCII letter or digit.
-func isAlpha(b byte) bool {
-	return b > '9'
-}
-
-// isAlphaNum returns true if the string contains only ASCII letters or digits.
-func isAlphaNum(s []byte) bool {
-	for _, c := range s {
-		if !('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || '0' <= c && c <= '9') {
-			return false
-		}
-	}
-	return true
-}
-
-// errSyntax is returned by any of the parsing functions when the
-// input is not well-formed, according to BCP 47.
-// TODO: return the position at which the syntax error occurred?
-var errSyntax = errors.New("language: tag is not well-formed")
-
 // ValueError is returned by any of the parsing functions when the
 // input is well-formed but the respective subtag is not recognized
 // as a valid value.
-type ValueError struct {
-	v [8]byte
-}
+type ValueError interface {
+	error
 
-func mkErrInvalid(s []byte) error {
-	var e ValueError
-	copy(e.v[:], s)
-	return e
-}
-
-func (e ValueError) tag() []byte {
-	n := bytes.IndexByte(e.v[:], 0)
-	if n == -1 {
-		n = 8
-	}
-	return e.v[:n]
-}
-
-// Error implements the error interface.
-func (e ValueError) Error() string {
-	return fmt.Sprintf("language: subtag %q is well-formed but unknown", e.tag())
-}
-
-// Subtag returns the subtag for which the error occurred.
-func (e ValueError) Subtag() string {
-	return string(e.tag())
-}
-
-// scanner is used to scan BCP 47 tokens, which are separated by _ or -.
-type scanner struct {
-	b     []byte
-	bytes [max99thPercentileSize]byte
-	token []byte
-	start int // start position of the current token
-	end   int // end position of the current token
-	next  int // next point for scan
-	err   error
-	done  bool
-}
-
-func makeScannerString(s string) scanner {
-	scan := scanner{}
-	if len(s) <= len(scan.bytes) {
-		scan.b = scan.bytes[:copy(scan.bytes[:], s)]
-	} else {
-		scan.b = []byte(s)
-	}
-	scan.init()
-	return scan
-}
-
-// makeScanner returns a scanner using b as the input buffer.
-// b is not copied and may be modified by the scanner routines.
-func makeScanner(b []byte) scanner {
-	scan := scanner{b: b}
-	scan.init()
-	return scan
-}
-
-func (s *scanner) init() {
-	for i, c := range s.b {
-		if c == '_' {
-			s.b[i] = '-'
-		}
-	}
-	s.scan()
-}
-
-// restToLower converts the string between start and end to lower case.
-func (s *scanner) toLower(start, end int) {
-	for i := start; i < end; i++ {
-		c := s.b[i]
-		if 'A' <= c && c <= 'Z' {
-			s.b[i] += 'a' - 'A'
-		}
-	}
-}
-
-func (s *scanner) setError(e error) {
-	if s.err == nil || (e == errSyntax && s.err != errSyntax) {
-		s.err = e
-	}
-}
-
-// resizeRange shrinks or grows the array at position oldStart such that
-// a new string of size newSize can fit between oldStart and oldEnd.
-// Sets the scan point to after the resized range.
-func (s *scanner) resizeRange(oldStart, oldEnd, newSize int) {
-	s.start = oldStart
-	if end := oldStart + newSize; end != oldEnd {
-		diff := end - oldEnd
-		if end < cap(s.b) {
-			b := make([]byte, len(s.b)+diff)
-			copy(b, s.b[:oldStart])
-			copy(b[end:], s.b[oldEnd:])
-			s.b = b
-		} else {
-			s.b = append(s.b[end:], s.b[oldEnd:]...)
-		}
-		s.next = end + (s.next - s.end)
-		s.end = end
-	}
-}
-
-// replace replaces the current token with repl.
-func (s *scanner) replace(repl string) {
-	s.resizeRange(s.start, s.end, len(repl))
-	copy(s.b[s.start:], repl)
-}
-
-// gobble removes the current token from the input.
-// Caller must call scan after calling gobble.
-func (s *scanner) gobble(e error) {
-	s.setError(e)
-	if s.start == 0 {
-		s.b = s.b[:+copy(s.b, s.b[s.next:])]
-		s.end = 0
-	} else {
-		s.b = s.b[:s.start-1+copy(s.b[s.start-1:], s.b[s.end:])]
-		s.end = s.start - 1
-	}
-	s.next = s.start
-}
-
-// deleteRange removes the given range from s.b before the current token.
-func (s *scanner) deleteRange(start, end int) {
-	s.setError(errSyntax)
-	s.b = s.b[:start+copy(s.b[start:], s.b[end:])]
-	diff := end - start
-	s.next -= diff
-	s.start -= diff
-	s.end -= diff
-}
-
-// scan parses the next token of a BCP 47 string.  Tokens that are larger
-// than 8 characters or include non-alphanumeric characters result in an error
-// and are gobbled and removed from the output.
-// It returns the end position of the last token consumed.
-func (s *scanner) scan() (end int) {
-	end = s.end
-	s.token = nil
-	for s.start = s.next; s.next < len(s.b); {
-		i := bytes.IndexByte(s.b[s.next:], '-')
-		if i == -1 {
-			s.end = len(s.b)
-			s.next = len(s.b)
-			i = s.end - s.start
-		} else {
-			s.end = s.next + i
-			s.next = s.end + 1
-		}
-		token := s.b[s.start:s.end]
-		if i < 1 || i > 8 || !isAlphaNum(token) {
-			s.gobble(errSyntax)
-			continue
-		}
-		s.token = token
-		return end
-	}
-	if n := len(s.b); n > 0 && s.b[n-1] == '-' {
-		s.setError(errSyntax)
-		s.b = s.b[:len(s.b)-1]
-	}
-	s.done = true
-	return end
-}
-
-// acceptMinSize parses multiple tokens of the given size or greater.
-// It returns the end position of the last token consumed.
-func (s *scanner) acceptMinSize(min int) (end int) {
-	end = s.end
-	s.scan()
-	for ; len(s.token) >= min; s.scan() {
-		end = s.end
-	}
-	return end
+	// Subtag returns the subtag for which the error occurred.
+	Subtag() string
 }
 
 // Parse parses the given BCP 47 string and returns a valid Tag. If parsing
@@ -223,7 +28,7 @@
 // ValueError. The Tag returned in this case is just stripped of the unknown
 // value. All other values are preserved. It accepts tags in the BCP 47 format
 // and extensions to this standard defined in
-// http://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
+// https://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
 // The resulting tag is canonicalized using the default canonicalization type.
 func Parse(s string) (t Tag, err error) {
 	return Default.Parse(s)
@@ -235,327 +40,18 @@
 // ValueError. The Tag returned in this case is just stripped of the unknown
 // value. All other values are preserved. It accepts tags in the BCP 47 format
 // and extensions to this standard defined in
-// http://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
-// The resulting tag is canonicalized using the the canonicalization type c.
+// https://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
+// The resulting tag is canonicalized using the canonicalization type c.
 func (c CanonType) Parse(s string) (t Tag, err error) {
-	// TODO: consider supporting old-style locale key-value pairs.
-	if s == "" {
-		return und, errSyntax
+	tt, err := language.Parse(s)
+	if err != nil {
+		return makeTag(tt), err
 	}
-	if len(s) <= maxAltTaglen {
-		b := [maxAltTaglen]byte{}
-		for i, c := range s {
-			// Generating invalid UTF-8 is okay as it won't match.
-			if 'A' <= c && c <= 'Z' {
-				c += 'a' - 'A'
-			} else if c == '_' {
-				c = '-'
-			}
-			b[i] = byte(c)
-		}
-		if t, ok := grandfathered(b); ok {
-			return t, nil
-		}
-	}
-	scan := makeScannerString(s)
-	t, err = parse(&scan, s)
-	t, changed := t.canonicalize(c)
+	tt, changed := canonicalize(c, tt)
 	if changed {
-		t.remakeString()
+		tt.RemakeString()
 	}
-	return t, err
-}
-
-func parse(scan *scanner, s string) (t Tag, err error) {
-	t = und
-	var end int
-	if n := len(scan.token); n <= 1 {
-		scan.toLower(0, len(scan.b))
-		if n == 0 || scan.token[0] != 'x' {
-			return t, errSyntax
-		}
-		end = parseExtensions(scan)
-	} else if n >= 4 {
-		return und, errSyntax
-	} else { // the usual case
-		t, end = parseTag(scan)
-		if n := len(scan.token); n == 1 {
-			t.pExt = uint16(end)
-			end = parseExtensions(scan)
-		} else if end < len(scan.b) {
-			scan.setError(errSyntax)
-			scan.b = scan.b[:end]
-		}
-	}
-	if int(t.pVariant) < len(scan.b) {
-		if end < len(s) {
-			s = s[:end]
-		}
-		if len(s) > 0 && tag.Compare(s, scan.b) == 0 {
-			t.str = s
-		} else {
-			t.str = string(scan.b)
-		}
-	} else {
-		t.pVariant, t.pExt = 0, 0
-	}
-	return t, scan.err
-}
-
-// parseTag parses language, script, region and variants.
-// It returns a Tag and the end position in the input that was parsed.
-func parseTag(scan *scanner) (t Tag, end int) {
-	var e error
-	// TODO: set an error if an unknown lang, script or region is encountered.
-	t.lang, e = getLangID(scan.token)
-	scan.setError(e)
-	scan.replace(t.lang.String())
-	langStart := scan.start
-	end = scan.scan()
-	for len(scan.token) == 3 && isAlpha(scan.token[0]) {
-		// From http://tools.ietf.org/html/bcp47, <lang>-<extlang> tags are equivalent
-		// to a tag of the form <extlang>.
-		lang, e := getLangID(scan.token)
-		if lang != 0 {
-			t.lang = lang
-			copy(scan.b[langStart:], lang.String())
-			scan.b[langStart+3] = '-'
-			scan.start = langStart + 4
-		}
-		scan.gobble(e)
-		end = scan.scan()
-	}
-	if len(scan.token) == 4 && isAlpha(scan.token[0]) {
-		t.script, e = getScriptID(script, scan.token)
-		if t.script == 0 {
-			scan.gobble(e)
-		}
-		end = scan.scan()
-	}
-	if n := len(scan.token); n >= 2 && n <= 3 {
-		t.region, e = getRegionID(scan.token)
-		if t.region == 0 {
-			scan.gobble(e)
-		} else {
-			scan.replace(t.region.String())
-		}
-		end = scan.scan()
-	}
-	scan.toLower(scan.start, len(scan.b))
-	t.pVariant = byte(end)
-	end = parseVariants(scan, end, t)
-	t.pExt = uint16(end)
-	return t, end
-}
-
-var separator = []byte{'-'}
-
-// parseVariants scans tokens as long as each token is a valid variant string.
-// Duplicate variants are removed.
-func parseVariants(scan *scanner, end int, t Tag) int {
-	start := scan.start
-	varIDBuf := [4]uint8{}
-	variantBuf := [4][]byte{}
-	varID := varIDBuf[:0]
-	variant := variantBuf[:0]
-	last := -1
-	needSort := false
-	for ; len(scan.token) >= 4; scan.scan() {
-		// TODO: measure the impact of needing this conversion and redesign
-		// the data structure if there is an issue.
-		v, ok := variantIndex[string(scan.token)]
-		if !ok {
-			// unknown variant
-			// TODO: allow user-defined variants?
-			scan.gobble(mkErrInvalid(scan.token))
-			continue
-		}
-		varID = append(varID, v)
-		variant = append(variant, scan.token)
-		if !needSort {
-			if last < int(v) {
-				last = int(v)
-			} else {
-				needSort = true
-				// There is no legal combinations of more than 7 variants
-				// (and this is by no means a useful sequence).
-				const maxVariants = 8
-				if len(varID) > maxVariants {
-					break
-				}
-			}
-		}
-		end = scan.end
-	}
-	if needSort {
-		sort.Sort(variantsSort{varID, variant})
-		k, l := 0, -1
-		for i, v := range varID {
-			w := int(v)
-			if l == w {
-				// Remove duplicates.
-				continue
-			}
-			varID[k] = varID[i]
-			variant[k] = variant[i]
-			k++
-			l = w
-		}
-		if str := bytes.Join(variant[:k], separator); len(str) == 0 {
-			end = start - 1
-		} else {
-			scan.resizeRange(start, end, len(str))
-			copy(scan.b[scan.start:], str)
-			end = scan.end
-		}
-	}
-	return end
-}
-
-type variantsSort struct {
-	i []uint8
-	v [][]byte
-}
-
-func (s variantsSort) Len() int {
-	return len(s.i)
-}
-
-func (s variantsSort) Swap(i, j int) {
-	s.i[i], s.i[j] = s.i[j], s.i[i]
-	s.v[i], s.v[j] = s.v[j], s.v[i]
-}
-
-func (s variantsSort) Less(i, j int) bool {
-	return s.i[i] < s.i[j]
-}
-
-type bytesSort [][]byte
-
-func (b bytesSort) Len() int {
-	return len(b)
-}
-
-func (b bytesSort) Swap(i, j int) {
-	b[i], b[j] = b[j], b[i]
-}
-
-func (b bytesSort) Less(i, j int) bool {
-	return bytes.Compare(b[i], b[j]) == -1
-}
-
-// parseExtensions parses and normalizes the extensions in the buffer.
-// It returns the last position of scan.b that is part of any extension.
-// It also trims scan.b to remove excess parts accordingly.
-func parseExtensions(scan *scanner) int {
-	start := scan.start
-	exts := [][]byte{}
-	private := []byte{}
-	end := scan.end
-	for len(scan.token) == 1 {
-		extStart := scan.start
-		ext := scan.token[0]
-		end = parseExtension(scan)
-		extension := scan.b[extStart:end]
-		if len(extension) < 3 || (ext != 'x' && len(extension) < 4) {
-			scan.setError(errSyntax)
-			end = extStart
-			continue
-		} else if start == extStart && (ext == 'x' || scan.start == len(scan.b)) {
-			scan.b = scan.b[:end]
-			return end
-		} else if ext == 'x' {
-			private = extension
-			break
-		}
-		exts = append(exts, extension)
-	}
-	sort.Sort(bytesSort(exts))
-	if len(private) > 0 {
-		exts = append(exts, private)
-	}
-	scan.b = scan.b[:start]
-	if len(exts) > 0 {
-		scan.b = append(scan.b, bytes.Join(exts, separator)...)
-	} else if start > 0 {
-		// Strip trailing '-'.
-		scan.b = scan.b[:start-1]
-	}
-	return end
-}
-
-// parseExtension parses a single extension and returns the position of
-// the extension end.
-func parseExtension(scan *scanner) int {
-	start, end := scan.start, scan.end
-	switch scan.token[0] {
-	case 'u':
-		attrStart := end
-		scan.scan()
-		for last := []byte{}; len(scan.token) > 2; scan.scan() {
-			if bytes.Compare(scan.token, last) != -1 {
-				// Attributes are unsorted. Start over from scratch.
-				p := attrStart + 1
-				scan.next = p
-				attrs := [][]byte{}
-				for scan.scan(); len(scan.token) > 2; scan.scan() {
-					attrs = append(attrs, scan.token)
-					end = scan.end
-				}
-				sort.Sort(bytesSort(attrs))
-				copy(scan.b[p:], bytes.Join(attrs, separator))
-				break
-			}
-			last = scan.token
-			end = scan.end
-		}
-		var last, key []byte
-		for attrEnd := end; len(scan.token) == 2; last = key {
-			key = scan.token
-			keyEnd := scan.end
-			end = scan.acceptMinSize(3)
-			// TODO: check key value validity
-			if keyEnd == end || bytes.Compare(key, last) != 1 {
-				// We have an invalid key or the keys are not sorted.
-				// Start scanning keys from scratch and reorder.
-				p := attrEnd + 1
-				scan.next = p
-				keys := [][]byte{}
-				for scan.scan(); len(scan.token) == 2; {
-					keyStart, keyEnd := scan.start, scan.end
-					end = scan.acceptMinSize(3)
-					if keyEnd != end {
-						keys = append(keys, scan.b[keyStart:end])
-					} else {
-						scan.setError(errSyntax)
-						end = keyStart
-					}
-				}
-				sort.Sort(bytesSort(keys))
-				reordered := bytes.Join(keys, separator)
-				if e := p + len(reordered); e < end {
-					scan.deleteRange(e, end)
-					end = e
-				}
-				copy(scan.b[p:], bytes.Join(keys, separator))
-				break
-			}
-		}
-	case 't':
-		scan.scan()
-		if n := len(scan.token); n >= 2 && n <= 3 && isAlpha(scan.token[1]) {
-			_, end = parseTag(scan)
-			scan.toLower(start, end)
-		}
-		for len(scan.token) == 2 && !isAlpha(scan.token[1]) {
-			end = scan.acceptMinSize(3)
-		}
-	case 'x':
-		end = scan.acceptMinSize(1)
-	default:
-		end = scan.acceptMinSize(2)
-	}
-	return end
+	return makeTag(tt), err
 }
 
 // Compose creates a Tag from individual parts, which may be of type Tag, Base,
@@ -563,10 +59,11 @@
 // Base, Script or Region or slice of type Variant or Extension is passed more
 // than once, the latter will overwrite the former. Variants and Extensions are
 // accumulated, but if two extensions of the same type are passed, the latter
-// will replace the former. A Tag overwrites all former values and typically
-// only makes sense as the first argument. The resulting tag is returned after
-// canonicalizing using the Default CanonType. If one or more errors are
-// encountered, one of the errors is returned.
+// will replace the former. For -u extensions, though, the key-type pairs are
+// added, where later values overwrite older ones. A Tag overwrites all former
+// values and typically only makes sense as the first argument. The resulting
+// tag is returned after canonicalizing using the Default CanonType. If one or
+// more errors are encountered, one of the errors is returned.
 func Compose(part ...interface{}) (t Tag, err error) {
 	return Default.Compose(part...)
 }
@@ -576,191 +73,63 @@
 // Base, Script or Region or slice of type Variant or Extension is passed more
 // than once, the latter will overwrite the former. Variants and Extensions are
 // accumulated, but if two extensions of the same type are passed, the latter
-// will replace the former. A Tag overwrites all former values and typically
-// only makes sense as the first argument. The resulting tag is returned after
-// canonicalizing using CanonType c. If one or more errors are encountered,
-// one of the errors is returned.
+// will replace the former. For -u extensions, though, the key-type pairs are
+// added, where later values overwrite older ones. A Tag overwrites all former
+// values and typically only makes sense as the first argument. The resulting
+// tag is returned after canonicalizing using CanonType c. If one or more errors
+// are encountered, one of the errors is returned.
 func (c CanonType) Compose(part ...interface{}) (t Tag, err error) {
-	var b builder
-	if err = b.update(part...); err != nil {
+	var b language.Builder
+	if err = update(&b, part...); err != nil {
 		return und, err
 	}
-	t, _ = b.tag.canonicalize(c)
-
-	if len(b.ext) > 0 || len(b.variant) > 0 {
-		sort.Sort(sortVariant(b.variant))
-		sort.Strings(b.ext)
-		if b.private != "" {
-			b.ext = append(b.ext, b.private)
-		}
-		n := maxCoreSize + tokenLen(b.variant...) + tokenLen(b.ext...)
-		buf := make([]byte, n)
-		p := t.genCoreBytes(buf)
-		t.pVariant = byte(p)
-		p += appendTokens(buf[p:], b.variant...)
-		t.pExt = uint16(p)
-		p += appendTokens(buf[p:], b.ext...)
-		t.str = string(buf[:p])
-	} else if b.private != "" {
-		t.str = b.private
-		t.remakeString()
-	}
-	return
-}
-
-type builder struct {
-	tag Tag
-
-	private string // the x extension
-	ext     []string
-	variant []string
-
-	err error
-}
-
-func (b *builder) addExt(e string) {
-	if e == "" {
-	} else if e[0] == 'x' {
-		b.private = e
-	} else {
-		b.ext = append(b.ext, e)
-	}
+	b.Tag, _ = canonicalize(c, b.Tag)
+	return makeTag(b.Make()), err
 }
 
 var errInvalidArgument = errors.New("invalid Extension or Variant")
 
-func (b *builder) update(part ...interface{}) (err error) {
-	replace := func(l *[]string, s string, eq func(a, b string) bool) bool {
-		if s == "" {
-			b.err = errInvalidArgument
-			return true
-		}
-		for i, v := range *l {
-			if eq(v, s) {
-				(*l)[i] = s
-				return true
-			}
-		}
-		return false
-	}
+func update(b *language.Builder, part ...interface{}) (err error) {
 	for _, x := range part {
 		switch v := x.(type) {
 		case Tag:
-			b.tag.lang = v.lang
-			b.tag.region = v.region
-			b.tag.script = v.script
-			if v.str != "" {
-				b.variant = nil
-				for x, s := "", v.str[v.pVariant:v.pExt]; s != ""; {
-					x, s = nextToken(s)
-					b.variant = append(b.variant, x)
-				}
-				b.ext, b.private = nil, ""
-				for i, e := int(v.pExt), ""; i < len(v.str); {
-					i, e = getExtension(v.str, i)
-					b.addExt(e)
-				}
-			}
+			b.SetTag(v.tag())
 		case Base:
-			b.tag.lang = v.langID
+			b.Tag.LangID = v.langID
 		case Script:
-			b.tag.script = v.scriptID
+			b.Tag.ScriptID = v.scriptID
 		case Region:
-			b.tag.region = v.regionID
+			b.Tag.RegionID = v.regionID
 		case Variant:
-			if !replace(&b.variant, v.variant, func(a, b string) bool { return a == b }) {
-				b.variant = append(b.variant, v.variant)
+			if v.variant == "" {
+				err = errInvalidArgument
+				break
 			}
+			b.AddVariant(v.variant)
 		case Extension:
-			if !replace(&b.ext, v.s, func(a, b string) bool { return a[0] == b[0] }) {
-				b.addExt(v.s)
+			if v.s == "" {
+				err = errInvalidArgument
+				break
 			}
+			b.SetExt(v.s)
 		case []Variant:
-			b.variant = nil
-			for _, x := range v {
-				b.update(x)
+			b.ClearVariants()
+			for _, v := range v {
+				b.AddVariant(v.variant)
 			}
 		case []Extension:
-			b.ext, b.private = nil, ""
+			b.ClearExtensions()
 			for _, e := range v {
-				b.update(e)
+				b.SetExt(e.s)
 			}
 		// TODO: support parsing of raw strings based on morphology or just extensions?
 		case error:
-			err = v
-		}
-	}
-	return
-}
-
-func tokenLen(token ...string) (n int) {
-	for _, t := range token {
-		n += len(t) + 1
-	}
-	return
-}
-
-func appendTokens(b []byte, token ...string) int {
-	p := 0
-	for _, t := range token {
-		b[p] = '-'
-		copy(b[p+1:], t)
-		p += 1 + len(t)
-	}
-	return p
-}
-
-type sortVariant []string
-
-func (s sortVariant) Len() int {
-	return len(s)
-}
-
-func (s sortVariant) Swap(i, j int) {
-	s[j], s[i] = s[i], s[j]
-}
-
-func (s sortVariant) Less(i, j int) bool {
-	return variantIndex[s[i]] < variantIndex[s[j]]
-}
-
-func findExt(list []string, x byte) int {
-	for i, e := range list {
-		if e[0] == x {
-			return i
-		}
-	}
-	return -1
-}
-
-// getExtension returns the name, body and end position of the extension.
-func getExtension(s string, p int) (end int, ext string) {
-	if s[p] == '-' {
-		p++
-	}
-	if s[p] == 'x' {
-		return len(s), s[p:]
-	}
-	end = nextExtension(s, p)
-	return end, s[p:end]
-}
-
-// nextExtension finds the next extension within the string, searching
-// for the -<char>- pattern from position p.
-// In the fast majority of cases, language tags will have at most
-// one extension and extensions tend to be small.
-func nextExtension(s string, p int) int {
-	for n := len(s) - 3; p < n; {
-		if s[p] == '-' {
-			if s[p+2] == '-' {
-				return p
+			if v != nil {
+				err = v
 			}
-			p += 3
-		} else {
-			p++
 		}
 	}
-	return len(s)
+	return
 }
 
 var errInvalidWeight = errors.New("ParseAcceptLanguage: invalid weight")
@@ -788,7 +157,7 @@
 			if !ok {
 				return nil, nil, err
 			}
-			t = Tag{lang: id}
+			t = makeTag(language.Tag{LangID: id})
 		}
 
 		// Scan the optional weight.
@@ -830,9 +199,9 @@
 	return strings.TrimSpace(s), ""
 }
 
-// Add hack mapping to deal with a small number of cases that that occur
+// Add hack mapping to deal with a small number of cases that occur
 // in Accept-Language (with reasonable frequency).
-var acceptFallback = map[string]langID{
+var acceptFallback = map[string]language.Language{
 	"english": _en,
 	"deutsch": _de,
 	"italian": _it,