Howard Miller

It's the 'Preferred language' setting (in preferences) of each user that defines the language they see.

It's got nothing to do with Moodle - your web server installation along with PHP is broken. Reinstalling Moodle will make no difference.

What to do next depends on how you're running (and installed) the web server (e.g. nginx, Apache etc) and PHP.

The user is separate from the database. So you can skip the 'CREATE USER' step if you intend to use the same user.

Why are you creating a database and then deleting it again? If you delete/drop a database then it's gone and you are starting again. In which case, the command you mentioned is correct. The reason for all the options is that if you don't do that you get your server defaults. This worked for you - *this time* - but is basically undefined. Use the options.

Isn't this more a limitation of iFrames?

Have you considered going down the road of having Moodle as an LTI provider ( Publish_as_LTI_tool ).

I've written a great deal of code in Vue (I'm not saying that makes me any kind of expert), but my solution was to embed the Vue application into a Moodle plugin (with a small Moodle amd module to 'glue' the two together).