How come this sentence doesn't mutate traeth to draeth unlike tafarn to dafarn?
traeth is masculine, so it does not mutate after 'r/y - traeth, y traeth
tafarn is feminine, so it does mutate - tafarn, y dafarn
Yes, it is really. Roughly 65% of nouns are masculine, so try to note those that are feminine.
There are some rough guides such as 'multi-syllable nouns that end in -aeth are feminine', but the there are always exceptions (gwasanaeth, gwahaniaeth,...) to any 'rule' to try and remember as well.
Just to keep it interesting for us all, a few nouns can be either, and a few vary with dialect or with meaning. And then there are the plurals...!
Well, in terms of French, you get used to hearing du lait to the point that de la lait sounds wrong so that's a way of remembering 'milk' is masculine. Depending on how often your going to be seeing/hearing Welsh, you'll get used to y tafarn sounding wrong etc. and you'll be able to remember it that way...or am I just blethering?