"I went home after they were married."
Translation:Es i adre ar ôl iddyn nhw briodi.
Mi is widely used in front of affirmative statements in some dialects, Fe in others, nothing in others. Both are optional anyway. If they are used, both cause soft mutation. Sometimes that soft mutation remains (optionally!) even when neither are used.
Mi/Fe gaeth hi ei harestio -> Gaeth hi ei harestio - She got arrested
Fe/Mi wnes i ddarllen llyfr ddoe -> Wnes i ddarllen llyfr ddoe - I read a book yesterday
I am only learning this language myself, but as I understand it, there is a 'mi' or a 'fe' in front of affirmative statements where a verb is conjugated. Even though this word is only said in some circumstances, it still performs a function in mutating the first spoken word of the sentence. It's silent, but still causes the mutation, the mutation remains as the word is still really there, even though it's invisible. Really it's 'gwnes i', the 'mi' mutates it to 'wnes i'. As I said I'm not an expert, this is just my current understanding, I may be wrong! you should probably consult a grammar book.
No, nothing at all to do with being a 'subject'!
To keep things simple, stop here and move on to the next practice. For the terminally curious and willing to get slightly complicated, read on...
Technically it (fe/mi) is known as an 'affirmative pre-verbal particle' or similar. It simply indicates the the verb that follows is an affirmative one (not negative or interrogative, which have their own pre-verbal particles, ni and a respectively). That is all that it is there for, nothing more complicated.
If fe/mi is used then it causes a soft mutation of the verb. Nowadays fe/mi is little used except in some dialects. Some colloquial forms of some verbs (ges, gest, gaeth, for example) keep the mutation even though people have stopped using the fe/mi particle.
To keep things simple while learning, just avoid using fe/mi yourself unless your neighbours do, and just be aware that you may see or hear them from time to time. Use ges, gest, gaeth etc because they are commonly used colloquially across Wales.