[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/web/about.go

@@ -39,6 +39,7 @@ func (m *Module) aboutGETHandler(c *gin.Context) {
 
 	c.HTML(http.StatusOK, "about.tmpl", gin.H{
 		"instance":         instance,
+		"languages":        config.GetInstanceLanguages().DisplayStrs(),
 		"ogMeta":           ogBase(instance),
 		"blocklistExposed": config.GetInstanceExposeSuspendedWeb(),
 		"stylesheets": []string{