gt-bad-language-pair: Unsupported translations consistency check

When Google Translate doesn't support translating from one language to another, it returns an error - this behavior differs from what happens when it does support a language pair but can't translate a specific sentence.

In the later, which is the most common scenario, it returns the source expression in the translation result. To make the behavior consistent in both scenarios, and allow the user to still see any definitions/images, mirror the later scenario when a language pair is not supported.

Return the results normally, replacing the language detection normally done by the `translate()` call by a specific call to `detect()` (also from Google Translate).

Note: Also removed the dirty hack the googletranslate library was using in that scenario, since Google Translate will never be able to translate the sentence when the language pair is unsupported.