Yes, there is an API to connect your integrations

No, you can add another language column and you will have another language available, check the example navbar, you have complete control over how you select and present the languages

There are only two moving parts on a site, the spreadsheets and html templates. The pages are very simple, you create and include templates that refer information on your spreadsheet, nothing is hardcoded on a block, you have complete contriol over the html, css and js.