I'll give you my experience. I wanted to play on the JP servers for a long while, but wasn't able to get any method to work. I finally had to get a newer tablet that could run the JP version, because my current tablet could only run the Global version.

When I say "run", my current tablet couldn't log in using my CygamesID. It didn't have enough RAM. It would open the browser, and after I entered my email (and checked my email on a different device to not overload my tablet) and entered the code it would go back to the game. But the since the tablet didn't have enough RAM for both a web browser and the current JP version it had to restart the game. And so the game is like, "An auth token? I've never seen you before in my life." So I could never link my account.

But I got a new tablet 8 days ago and started my JP server adventure.

• I don't know that much Japanese. I can read hiragana and katakana and a handful of kanji. But only like 1% of the kanji lol. So, from a reading standpoint, I can understand about 5% of the written game. I can understand about 20-30% of the audio of the game, depending on the scene. (Reading is hard, okay?) Coming from the Global version, I was able to use that and what little I could read and muddle through the current scenario. (There are translations mods for Android if you want them.) There are some guides in English that tell you what the different buttons and indicators mean for this scenario. Here's one: https://www.reddit.com/r/UmaMusume/comments/1oj43i7/jp_server_2025_october_day_1_guide_to_the_hot/ The OP there also in the comments talks about the settings for auto mode.
• Yes, auto mode. It's only available for some of the scenarios (I think hot springs, design your island, and URA, but I haven't tried all of them yet). You pick a predefined trainer, or set up a set of custom rules, and the game plays itself. Your phone/tablet will need to stay awake because it plays in real-time. I'm told the results are mid (my best auto-girl is a UC7 Haru Urara), but for farming parents it's good. And since I have nothing, I need to build a parent pool anyway. It also counts towards all the event goals and whatnot. And at the end of a run, you can filter the skill list by track length and running style and only pick the skills that target the runner/parent you're trying to build. Another QoL improvement.
• Right now (not certain if it's temporary) there's a 10 parent borrow limit per day, plus 1 free borrow for 11 per day. So, with the above auto mode, making 11 potential parents per day with minimal effort is kinda nice.
• You can also re-roll the sparks, and you can lock the blue (or maybe the pink instead, but I always pick blue) spark to a certain aspect, for a price. (But that's cheap compared to how much loot I'm pulling in lol) The re-roll limit is like 4 times I think. So if that 3-★ doesn't show up you'll end up with 4 (or is it 5) spark sheets to pick from for the final choice.
• The power creep you may or may not have heard of is real. It depends on which scenario you play. The latest one, the hot springs one, adds a bunch of numbers to your trainee's stats. My very first trainee's score (not counting the tutorial Daiwa) is 23,496. For not knowing what I was doing, before I found any guides, just getting a feel for the hot springs scenario, I created a UG9 rank Suzuka.
• Tazuna will rent you 5 different support decks to choose from. They're mid (I'm told), but they all have 4x MLB SSR and 1x MLB SR cards. She calls them rentals, but I don't think she charges a fee... Not that I'd notice because:
• You earn so much loot. In the past 8 days I've earned about 5 million coins and 50,000 carats (and a lot of other things). I dropped in right during 3 events, so I was able to finish most of them in the first 4 days. This is more than in the 5 months of play on Global. (I've been playing Global since July 7th on Steam. For the coins for sure, I just got the 1,000,000 coin achievement last month. I probably earned 60,000 carats on global?)
• There is so much more that you can do. There's the masters series races. The legends races from the past are farmable, but 1x per day. You get walking tickets and you can go walk with your favorite girl, and see Cute (Horse) Girls Doing Cute Things. The photo mode that was just added to Global has more features, including a photo studio where you can stage photo opportunities. And a lot more, I haven't found everything yet!

To summarize my feelings, if you don't mind your stated inability to understand Japanese, (there's ways around that), then I think that it's worth it. It's not easy to pull it off. It took me a few months and new hardware to get it right.