I always check that dialogue is adding something to the story, showing personality or creating atmosphere. It’s good if it’s doing at least two of those things if not all three. It shouldn’t sound too natural – natural dialogue can be very pedestrian - yet each piece should sound as if it really is spoken by the character who is supposed to be saying it. It should be possible to pretty well identity who is speaking even if there is no tag word there.
So, I also check whether I’ve overused tag words. Sometimes they’re not needed at all – if only two people are speaking for instance and if it doesn’t go on for more than about a page. Sometimes they can be replaced with some body language or a small action. And “said” is the best though whispered, shouted, asked, and replied might also be all right.
Dialogue presents some special challenges in this text. I want my Welsh character to speak with a Welsh accent. So, I’m reading bits out loud every time I check. I think I’ve got it.
I have a few phrases in Welsh but I think their meaning is clear because of the content and how people react to them
Helga wills till have a bit of German accent. She uses a few German words, in particular Liebling which finds an echo in some character using the Welsh equivalent, cariad. There are some food items and relations as well. She still get confused with the half hour; “half two” in German means half way towards two i.e. half past one.
Whole chapters are constructed in her voice yet dialogue with them must be in standard English because the characters were speaking in standard German.
A dilemma throughout this cycle has been can I use modern English to represent 1940s’ German. Or must I make it sound like 1940s’ English? I have gone for the former. The way they spoke would have been as natural to them as modern English is to us. I’ve even used the term “bro” for bother. It seemed to fit the relationship exactly.