So in my book, I have a country named Tir Dreigiau, which is Welsh for "land of dragons". Tir Dreigiau's "enemy" has a princess named Grug, which is also a Welsh name. It means "heather". So, is it ok for names from different countries to have the same origin?
Time for a mental calculation. Out of 100, how significantly would this ruin the enjoyment of an expert reading your book? Now, out of 100, what percentage of your audience is likely to be an expert. Add the two, and consider the result. More example, I have a character whose father is in prison in the UK. He's a Polish national so, according to my research, he'd be deported after his sentence. This is not the case in the book. If the book is read by someone who knew that, I'd estimate maybe 20 annoyance points. It's not really important to the plot, but it does come up. Now, I'd guess maybe 5% of readers would spot that inaccuracy. That makes for 25 total. Insignificant. Once you start getting to the 70s and over, you have a problem.
Agreed with @NiallRoach. Seriously, how many people would even know outside of Wales? It may be knowledge you possess because of heritage or you researched it, but it's not something the average Joe/Jane is even going to be aware of. When we do research for a book, sometimes we get what I call "grad student syndrome". I was a grad student for a couple of years before I got tired of the whole thing, and I remember feeling - at least for that first post-grad year - that the sun rose and set on the information I was studying, that nothing was more important than this, and being consumed with frustration when others either failed to see it or were ignorant of the subject. How could they not know and be struck dumb by the universe-altering importance of what I am learning?!?!?!? That's grad student syndrome.
Another thing to consider is whether, down the line, the two rival nations have a common ancestry in some way? While the language & customs may have evolved differently by separation, specific interactions with various surrounding cultures through trade/war/etc., having a common ancestry & root language can be an easy enough explanation in similiar names and so forth I had a collaboration project once where I had two main countries, and the one had Russian/Eastern European style names while the other had Urdu/Hindi style names. Some of the surrounding nations of the latter who had a shared ancestry also had Farsi/Urdu style names, regardless of whether they were allies or enemy states I realize that most people didn't care or think too deeply about this, but I liked having differentiating sounds between the nations & basing it on other regional languages made it simple for me to keep track of So it's something you can consider if you're interested
Or something simpler: one or both of Grug's parents could be from Tir Driegiau or visited at some point and picked up the language, or they could've just heard the name and liked it. Really, I don't know Welsh from Arabic, so something like that would pass right by me.
Sure I don't see why not. Their cultures would have bumped into at some point in their history. If they are neighboring nations then it is not uncommon for them to exchange certain aspects. If they are radically far apart, then it would be less likely to none at all in the way of exchanging any cultural attributes. Then it might look a little funny, or if they are radically different cultures altogether. Look at Latin, the grandfather of many of the Western languages. Ergo all these languages have a common ancestor. So you have to decide if there was a point in time the two nations were civil in the past, or some of their people migrated from one to the other. This could account for the similarity of your princess having a name in the enemies tongue. Find the things that would build a foundation for the answer that you seek, you just have to look in the obscurity beyond that which you have placed in front of yourself. Simple really.
i don't see this as a problem - look at latin america - numerous countries with either spanish or portuguese roots to their names etc from a colonial past - same with canada and the US , and so on.... May Tir Dreigau and its neignour were settled by welsh astronauts (or more believably may be tir dregau once ruled its neighbour or vice versa)
Nobody is missing that point. The question was about using the same language base for two different nations, not about our opinion of the name. If writing is art, then it's the artist's perogative to name their charactes whatever they like.
I think it was meant in jest. But to get back on topic, I don't think there's a problem unless the fact that both names derive from the same language is important to the story. If you just like the names for how the sound then who's to make any judgement at all about the fact that they derive from a language in the real world. In The Lord of the Rings there is such a strong connection between welsh and elvish that it becomes quite an important fact. In your case where there are two names, I don't think you need to worry.
I mean, if the two countries are close together, it's only natural that there would be intermingling between them, right? All it takes is one Tir Dreigiau man to have defected on enemy shores and started a life with an enemy woman, and bam, throw in 100 years and the culture has spread just a little. I wouldn't worry about names too much! With something like this, you can always add in a reason later. Don't let it put a stopper in your creativity!
I'd be unenthusiastic if this story was actually about historical Wales and Grug was the princess of a non-Welsh-speaking enemy of Wales. But it's not. It's fantasy, so go for it.