We aren't teaching English here, we are teaching Gaelic. This is the way I would express this as an English speaker on the West coast of Scotland. There are many examples in the course where the English used is non standard as it is often not possible (or desirable to try) and convey the Gaelic meaning using "standard English". The OED lists this as an adjective so we will likely continue to use it. NOTE - I have edited as my initial response came across as ruder than I would have hoped.
Fair play, my comment was overly snippy. No need. The Oxford English Dictionary lists fun as an adjective and "so fun" is definitely something we say in the West Coast of Scotland, possibly influenced by Gaelic. It also mirrors the Gaelic most closely and the various suggested alternatives I have seen for this do not adequately give the meaning. There are many examples of non standard English in the course. This is absolutely necessary to accurately convey meaning in Gaelic and it is unfortunately beyond the scope of the course / software to convey the idiom of Gaelic / differences in Gaelic tenses and also provide standard English that you would want an English learner to pick up.
I answered Tha i cho sporsail, expecting the translation to be "She is so fun." This was a 'hit the key with the word on it' question, not a 'type in the answer question.' I was given a "Nicely done!" correct response for my 'i' but the translation was 'I am so fun.' I suspect either a technical difficulty, or I don't understand how the I/me pronoun works.
Can anyone weigh in, (especially if it's my misunderstanding how the pronouns work)?