Even if having a custom translation is less useful it's still valid in some scenarios. So instead of just throwing this should be a warning that defaults to throwing.

Or we can do that when we introduce a better API to set the translation.

We don't use custom translation in query. (We cannot use it either till API is changed). So throwing is better than warning and then ignoring it.

Please avoid merging more than 2 PRs per 30 minutes to master