"After you wash your hands we are eating supper."
Translation:Ar ôl i chi olchi eich dwylo dyn ni'n bwyta swper.
This sentence sounds amazing! It really vibrates your throat and rolls of the tongue.
The use of the present tense in the second part of this sentence does not make sense, to my mind. The first part ("ar ol i...", "after you wash...") is tense-less. But the word "after" indicates that the eating of the supper has not yet taken place. In the English, although the present tense is used, the sense is future - ie, after you wash your hands, we WILL eat supper. Surely in the Welsh translation the future tense should be used in the second part of the sentence?
Using the future tense in the second half (we will eat supper) has a slightly different nuance than using the present tense, but both are correct. The way the sentence is written, the emphasis is on eating and implies a sense of immediacy - we are eating supper (rather than going for a drive, watching tv, etc) but you've got to wash your hands first and we're all waiting for you to do so because we're all ready to start eating. If you use the future tense, the emphasis is on the order of the events - first you wash your hands, then we'll eat, then we'll do something else. There is no sense of urgency (we're not all sitting around waiting for you to clean up) and there even could be a slight delay between the washing and the eating (you wash up, then the table will get set and eventually we'll get around to eating).
If you're going from Welsh to English, either translation would work, but there's nothing inherently wrong with using present tense vs. future in the English sentence.