This is probably a symptom of the Welsh course being more geared towards British English than a lot of other courses. A British person would understand "taken"in this context but rarely use it this way.
Since eto translates both as 'yet' and as 'again', in the sentence 'Have you had a bath again?' would a different adverb be used for 'again'?
Or would eto be used in a different position?
Or would the sentence remain unchanged (which of the two meanings of eto is correct would be understood from the context of speech)?
The problem here is that in British English as in Welsh we'd say "Have you had a bath yet?" i.e. the perfect tense. What's translated as "Did you have a bath?" is formed in a different way in Welsh i.e. the simple past, and wouldn't be used in this sentence either.
So although you're correct, it's best to think of this as "Have you had" and you'll learn "Did you have" later in the course. Otherwise you might get into confusion.
Nevertheless, teaching things wrong is always going to confuse people more. Sooner or later you have to teach people that the "elasticity" of a tense in English will not always be identical to that of its nearest equivalent in Welsh (or any other language). I go for sooner rather than later. However, teaching people that there's a mysterious difference between the past simple and present perfect simple in English in this context is clearly no way to focus on the target language.
Yep, the past tenses (perfect, simple past, imperfect, pluperfect) are usually used in exactly the same in Welsh as they are in British English, so for most learners it's not an issue. American English sometimes has slightly different usage so this is where this particular problem arises and where American learners need to pay attention to the differences found in Welsh.
Not sure what cael stands for exactly. Can I say: "Dw i wedi cael te a tost heddiw." Or is does it only work in the contest of having done something? If that makes sense.
It's used with the word bath to make the phrase cael bath "have a bath" or with food or drink to mean "have toast/tea/whatever", similar to English. It can be used in any tense. Not sure if that answers your question?