Hey @kariforuniajin !
In this sentence, 行く is conjugated using たい to create 行きたい ‘want to go’ and くなる is added to create 行きたくなる ‘I ended up wanting to go to the bathroom’. When the grammar point になる・くなる is attached to a verb conjugated using たい it will follow the conjugation rule of a い-adjective since たい is conjugated in the same way as い-adjectives.
We hope this clears it up!
Hey everyone, first post here 
In the example sentences, why is
お茶が冷たくなっているよ。
translated as
„The tea got cold.“
instead of
„The tea is getting cold.“
I somewhat understand that the てなる form can have both meanings, but I don‘t get why only one of the two is chosen here as the explanation, as the meanings are very different.
Thanks!
Hey @Yokokun !
This sentence is translated as ‘The tea got cold’ because of the ている that is used in this sentence. As explained in this grammar point, in Japanese, when something exist in the state of being something (cold in this example) it will stay in that state. This means that the tea is not ‘getting cold’, but it has stopped being warm, and now it exists in the state of being cold.
Hope this answers your question!
Thanks for your answer!
I‘m still not sure I fully get it, though. The ている is attached to and modifying なる, so the literal meaning - as I understand it - would be „is in the state of becoming“, therefore „is becoming/getting cold“.
If the intended meaning is „got cold“, why not use „つめたくなったよ。“ instead, like in one of the other examples „コーヒーが温くなった。“ ?
Or is there a difference in nuance in English between „got“ and „has become“ I‘m not getting (as a non-native speaker) here?
And if what I actually want to say is „the tea is (in the state of) getting cold“ which construction would I use in Japanese?
(Sorry I‘m deep diving so much into this, I just have a hard time wrapping my head around this.)
The difference between 冷たくなっているよ and 冷たくなったよ is the nuance and similar to how ‘has become’ and ‘became’ have a slight difference in nuance. 冷たくなっているよ has the nuance of ‘it has become cold’, and 冷たくなったよ has the nuance of ‘it became cold’. With 冷たくなっているよ the tea is still in the process of getting cold, while with 冷たくなったよ, just focuses on the fact that it got cold sometime in the past.
To express ‘the tea is (in the state of) getting cold’, 冷たくなっている would be best to use!
I hope this clears it up!