No, 阿拉伯海 would be the Chinese name for the Arabian Sea. The Japanese pre-modern term would sometimes be アラブの海 or 西印度洋 (Arabia-kai and Sei-Indoyō respectively). In this case, Meiji Japan would've been modernizing its geographic naming conventions and so アラブの海 would suffice. Other seas would be written using Kyūjitai, for example 南支那海 (South China Sea), 太平洋 (Pacific Ocean), 印度洋 (Indian Ocean), 波羅的海 (Baltic Sea). As you can see, it's on a case-by-case basis. I'd be happy to connect and assist over discord or steam messages!

No problem at all and I appreciate that you pointed that out, I wasn't aware that there was an older form of Japanese. I'll make an updated version of the mod in the next few days. I do have one question, would the seas be written in Kyujitai too? So for example, would it be 阿拉伯海 instead of アラブの海? Thanks

Hope I'm not coming off as nitpicking, but wouldn't countries at the time be listed in Kyūjitai? Example: UK = 英國 instead of イギリス, Dai Nam = 越南 instead of トンキン, Siam = 暹羅 instead of シャム, and Europe = 欧州 instead of ヨーロッパ. If you'd like more assistance I'd be happy to help! The map looks great and I hope to make it a little more immersive!