[feature] Set/show instance language(s); show post language on frontend (#2362)

* update go text, include text/display

* [feature] Set instance langs, show post lang on frontend

* go fmt

* WebGet

* set language for whole article, don't use FA icon

* mention instance languages + other optional config vars

* little tweak

* put languages in config properly

* warn log language parse

* change some naming around

* tidy up validate a bit

* lint

* rename LanguageTmpl in template

internal/config/defaults.go

@@ -22,6 +22,7 @@ import (
 
 	"codeberg.org/gruf/go-bytesize"
 	"github.com/coreos/go-oidc/v3/oidc"
+	"github.com/superseriousbusiness/gotosocial/internal/language"
 )
 
 // Defaults contains a populated Configuration with reasonable defaults. Note that
@@ -62,6 +63,7 @@ var Defaults = Configuration{
 	InstanceExposeSuspended:        false,
 	InstanceExposeSuspendedWeb:     false,
 	InstanceDeliverToSharedInboxes: true,
+	InstanceLanguages:              make(language.Languages, 0),
 
 	AccountsRegistrationOpen: true,
 	AccountsApprovalRequired: true,