[feature] Allow full BCP 47 in language inputs (#2067)

* Allow full BCP 47 in language inputs

Fixes #2066

* Fuse validation and normalization for languages

* Remove outdated comment line

* Move post language canonicalization test

1 files changed, 11 insertions, 6 deletions

diff --git a/internal/validate/formvalidation.go b/internal/validate/formvalidation.go
index 76ce6a8de..1b5996b4b 100644
--- a/internal/validate/formvalidation.go
+++ b/internal/validate/formvalidation.go
@@ -99,14 +99,19 @@ func Email(email string) error {
 	return err
 }
 
-// Language checks that the given language string is a 2- or 3-letter ISO 639 code.
-// Returns an error if the language cannot be parsed. See: https://pkg.go.dev/golang.org/x/text/language
-func Language(lang string) error {
+// Language checks that the given language string is a valid, if not necessarily canonical, BCP 47 language tag.
+// Returns a canonicalized version of the tag if the language can be parsed.
+// Returns an error if the language cannot be parsed.
+// See: https://pkg.go.dev/golang.org/x/text/language
+func Language(lang string) (string, error) {
 	if lang == "" {
-		return errors.New("no language provided")
+		return "", errors.New("no language provided")
 	}
-	_, err := language.ParseBase(lang)
-	return err
+	parsed, err := language.Parse(lang)
+	if err != nil {
+		return "", err
+	}
+	return parsed.String(), err
 }
 
 // SignUpReason checks that a sufficient reason is given for a server signup request