Every time I have to type the content somewhere else and then copy-paste that here in the editor. Therefore, it will be great if we get a multi-lingual keyboard in the Stack Exchange editors.
For installing a keyboard functionality with multilingual support to the editor will require resources.
What I suggest use on screen keyboard and download language packs as your demand and change type settings if you are using windows. Your keyboard will change font like this,
And for mobiles and tablets there are apps like this which comes in handy.
Mi Yodeya has a built-in Hebrew keyboard, which was added in 2013 as an experiment. We're very happy with it. I don't know what discussions, if any, have been had since then about expanding this to other languages, but someone who was at the time a product manager for SE left the door open to expanding to other languages.
While you're waiting, you could adapt the user script that predated the built-in feature to your language of choice.
Adding keyboards for other alphabets should probably be done only on sites where a particular alphabet is frequently needed in writing about that site's topic. Otherwise, you might end up with a proliferation of keyboard buttons cluttering up the UI on general sites. For the occasional word needed from another alphabet, it's better to use other tools; if that's a frequent need, you should consider adding it to a site.
Edit: I just noticed that you said "to write questions and answers". As this answer notes, the language of the network is English. On some sites it's important to also be able to provide content in other languages -- most notably the language sites, but also others -- but you shouldn't be composing your entire post in a language other than English except on the language-specific Stack Overflow sites.
This should be a system level thing, not a website level thing.
Considering that outside a handful of specialist or language sites - the use for this is somewhat minimal, and outside the Russian/Portuguese SO site, various language sites and to a small extent judaism (where questions are in english, but there's a definite need for some content in other scripts) - english is the primary language of the network.
In addition, non latin languages are complicated. There's different scripts, RTL and LTR writing, synthetic languages (Quenya and Klingon for example might belong in literature or movies) not all of which have unicode support.
Moderation is another issue. I'm not going to be able to tell the difference between poetry and toilet scribbles in a language I don't get, and I might not be able to grab the right person to tell me what's the difference.
And well, even where non english languages are supported, in the UIs I've never seen sites have localised keyboards for their own scripts. My dad runs facebook in tamil, and at one point had google in tamil - which had me translating terms back and forth, and mostly being confused.
Creating such keyboards the right way... would need developers who are intimately familiar with the language and online culture of the place. Google has 5 tamil keyboards on their input options for example -so picking what to support is going to be a pain. You'd also have trouble checking if output is correct.
This is going to be a massive amount of work, for almost no real benefit, even if you prioritized developers to do such things.
And well, the work's mostly done elsewhere.
I've found that google has a robust set of tools for android and Wintel PCs (and apparently a chrome browser plugin) - My mom used their transliteration keyboard for quite a while on windows, and uses it on android as well.
It also covers a small subset of indian languages (though presumably the 'common' scripts). I'm pretty sure most languages should have native keyboards or trivially installable support.