Translation:We are washing the dog because it is dirty.
Does Finnish ever use "hän" for non-human animals? Especially a known individual animal like a family dog?
If not, is this because in spoken or informal Finnish there is a tendency to use "se" for humans as well, so the issue of whether to use "hän" or "se" doesn't really arise?
There is no comma before "because" in this sentence in English. Subordinating conjunctions are not preceded by commas (unless whatever precedes them has to be set off from the rest of the sentence by commas). Subordinate clauses do not need a comma at the beginning in English as the conjunction is sufficient. There is a comma at the end of a subordinate clause if it precedes the subject. (If it precedes the subject, there is a comma at the end of a subordinate clause.)
It's completely trivial, but I can't report it as anything but "Something else went wrong," so I'm mentioning it here.
I'm assuming commas are needed on both sides of a subordinate clause in Finnish, as in German?