Unify criteria in prefixes of dictionary names

[jmaraujouy]

Nikolaj, what do you think of the idea of simplifying the prefixes used in dictionary file names, so that they all use the same code?

Right now we have some dictionary files that uses "en_" while others have "eng_" prefixes; we also have "es_" and "spa_" for spanish; "fr_" & "fra_" for french; "se_" and "swe_", "pt_" and "por_", just to name a few...

https://github.com/SubtitleEdit/subtitleedit/tree/main/Dictionaries

Either using two or three letter country codes, but all of them using the same criteria?