diff --git a/app/controllers/LilaController.scala b/app/controllers/LilaController.scala
index 937e11dd01..c86a1447d3 100644
--- a/app/controllers/LilaController.scala
+++ b/app/controllers/LilaController.scala
@@ -41,7 +41,6 @@ private[controllers] trait LilaController
       api = _ => fuccess(Ok(jsonOkBody) as JSON)
     )
 
-  // implicit def lang(implicit req: RequestHeader) = Env.i18n.pool lang req
   implicit def lang(implicit ctx: Context) = ctx.lang
 
   protected def NoCache(res: Result): Result = res.withHeaders(
@@ -352,8 +351,21 @@ private[controllers] trait LilaController
     else if (HTTPRequest isBot ctx.req) fuccess(NotFound)
     else result
 
-  protected def errorsAsJson(form: play.api.data.Form[_])(implicit lang: play.api.i18n.Messages) =
-    lila.common.Form errorsAsJson form
+  private val jsonGlobalErrorRenamer = {
+    import play.api.libs.json._
+    __.json update (
+      (__ \ "global").json copyFrom (__ \ "").json.pick
+    ) andThen (__ \ "").json.prune
+  }
+
+  protected def errorsAsJson(form: play.api.data.Form[_])(implicit lang: play.api.i18n.Lang) = {
+    val json = Json.toJson(
+      form.errors.groupBy(_.key).mapValues { errors =>
+        errors.map(e => lila.i18n.Translator.txt.literal(e.message, e.args, lang))
+      }
+    )
+    json validate jsonGlobalErrorRenamer getOrElse json
+  }
 
   protected val pgnContentType = "application/x-chess-pgn"
 }
diff --git a/modules/common/src/main/Form.scala b/modules/common/src/main/Form.scala
index 306b57133f..2ea0bf78d1 100644
--- a/modules/common/src/main/Form.scala
+++ b/modules/common/src/main/Form.scala
@@ -4,7 +4,6 @@ import org.joda.time.DateTimeZone
 import play.api.data.format.Formats._
 import play.api.data.format.Formatter
 import play.api.data.Forms._
-import play.api.libs.json._
 
 object Form {
 
@@ -39,13 +38,6 @@ object Form {
   private def pluralize(pattern: String, nb: Int) =
     pattern.replace("{s}", (nb != 1).fold("s", ""))
 
-  private val jsonGlobalErrorRenamer = __.json update (
-    (__ \ "global").json copyFrom (__ \ "").json.pick
-  ) andThen (__ \ "").json.prune
-
-  def errorsAsJson(form: play.api.data.Form[_])(implicit lang: play.api.i18n.Messages) =
-    form.errorsAsJson validate jsonGlobalErrorRenamer getOrElse form.errorsAsJson
-
   object formatter {
     def stringFormatter[A](from: A => String, to: String => A): Formatter[A] = new Formatter[A] {
       def bind(key: String, data: Map[String, String]) = stringFormat.bind(key, data).right map to
diff --git a/modules/security/src/main/DataForm.scala b/modules/security/src/main/DataForm.scala
index 7f549276d0..6eb07f2774 100644
--- a/modules/security/src/main/DataForm.scala
+++ b/modules/security/src/main/DataForm.scala
@@ -42,7 +42,7 @@ final class DataForm(
         regex = """^[^\d].+$""".r,
         error = "usernameStartNoNumber"
       )
-    ).verifying("", u => !UserRepo.nameExists(u).awaitSeconds(4))
+    ).verifying("usernameAlreadyUsed", u => !UserRepo.nameExists(u).awaitSeconds(4))
       .verifying("usernameUnacceptable", u => !LameName(u))
 
     val website = Form(mapping(