American- or British English are two variations of the English language. They have substantial differences. They are sufficiently the same and are unlikely be mistaken to be separate languages.
In OmegaWiki, it has been possible to add entries for English; this meant there is no difference between written the different versions of English or you had to specify both versions. Issues like this exist for other languages like Serbian and Mandarin as well.
In the OmegaWiki user interface, languages are considered ISO-639 entities. When a DefinedMeaning for a language is part of the appropriate collection, we use the translations in our user interface. The problem is that all these linguistic entities are needed now and that they are created to make OmegaWiki work.
For the ISO-639-6 there will be issues as the codes we make, using the RFC 4646 methodology, will be replaced. It will also be interesting to learn how in the end everything will be merged together.
In the mean time we now support localisation for these linguistic entities.