Yes. Last I checked, it isn't available in the US store yet.
When you first set up your Switch, it asks for your display language preference. If the game supports the default language you set your system as, it automatically sets its language that way.
As far as Trinity goes, there's just a disclaimer splash screen in complete Japanese. Everything else after that is totally in English, except there IS a voice clip sound pack for effects where dialogue is in Japanese. Not sure if the US release will be keeping those or not.
The cross platform thing was brought up in a press release previously, I think? It may be just as you say, but I'll dig around on the matter further and see what I find. At the moment, the community portal is completely empty. Not sure if it's because the portal is faulty or no one's pushed anything out yet.
The performance issues, I suspect, are related to how the software handles a few things. Loading between editor and game is normal-the system does have to compile and build the project to run it.
The loading between Editor and DB manager is unusual, but what I suspect is the application loads/saves the entire DB together. After a while, it bothered me less and less, really.
What brand of SD card are you using? Applications do have a noticeable difference in speed when installed into an SD card vs internal memory, but also the Switch is known to be very finnicky about the hardware you attach to it.
I used a first party 128gb card. Haven't really built heavily on Trinity yet, so mileage varies here, but I've yet to encounter a total software freeze.
I really wouldn't dream of plugin support for these console releases ever, as it feels to me like that would just open a wealth of hardware and software issues the developers and console manufacturers just wouldn't want to deal with.
I personally don't mind living without it. Having grown up on RM2k, I can get behind more traditional-playing games. The RTP may get grating after a while, but much like with RM on 3DS, I look forward to enjoying bite-sized community-made games on-the-go.
I think the more limited options allow creators to focus on just crafting a good story.
My one concern with post 2k3 RM was paralysis from too much freedom. Projects stall becase some people just can't get the custom materials and features they want thrown in. With console releases, you work with what you have. Less distractions, and yes, much more beginmer friendly since it's far less intimidating (at least, if you're not too bothered about having to build and write an entire RPG with console controllers).