Modify the "warning" message when looking up for languages not supported
"Correct" can mean many things, indeed; it surely doesn't mean "ISO-valid" here. Is this code on CLDR? If not, I doubt it can be checked anywhere. Do you have proposals for a wording? Remember that it would be the same on other wikis using Translate.
The code given was only an example. I don't know if there is a technical way to have a different message if the code searched is really an invalid ISO code or if it is a valid ISO code that is not supported by translatewiki.
How about an alternative wording "The language code is not recognised or is disabled" (the message appears both where no portal exists and where the language has been disabled (example). Perhaps we could link with the help page Translatewiki.net languages with a link text something like "Read about languages supported at translatewiki.net and request a new language".