noto-fonts VS MarathiCursive

What I'm personally using for this is Noto (short for "no tofu," with "tofu" referring to the missing character glyphs), accessible with noto-fonts and noto-fonts-extra (there's also noto-fonts-emoji which might be useful), though each pretty much needs to be added as a fallback separately. For CJK / Han characters, Babelstone (at babelstone-han) has good coverage, though the version in Nixpkgs isn't quite up to date so you may want to get a newer one from their website. If you really want complete Unicode coverage, the last font that I know of that you'd want is Hanazono. Hanazono isn't in Nixpkgs at all, and comes in two parts: HanaMinA and HanaMinB.

In a font that supports multiple writing systems, whether Latin, Cyrillic, or even Chinese/Japanese/Korean characters, the glyphs from different systems should be designed to harmonize. Having different visual weights is incorrect. See Google's Noto font family, for example.

Noto Sans

I use Iosevka for the terminal emulator and the editor. And Noto for the rest.

I saw a post from 2015 saying they are adding a font combing all the noto fonts from a region like south asia, is it done?

I would think as long as you use a font that supports both languages, Gramps should be able to display either. The interface would need to be in one or the other, but things like names and notes could be either and still display properly as long as the font supports it. Noto Sans is one good choice for multiple languages.

I checked recent commits on Google's Noto fonts repo (https://github.com/googlefonts/noto-fonts/blob/main/hinted/ttf/NotoSans/NotoSans-Italic.ttf) and the version of NotoSans-Italic for all of the three commits after November 3, 2021 seems fine, at least when opened in KFontView or FontForge. Assuming the Arch package uses the same data as the Github repo, this is not an upstream issue (unless I missed something, of course).

Luckily for us, Ren'Py has an easy way to support this problem. You can have several fonts, and define which langage use which font. Either you find fonts that are visually fitting together (looking "modern" or not, etc). Or you can use something like Google's Noto collection of fonts that has fonts for most langages. You can use "noto serif" for latin langages, "noto serif japanese" for the japanese translation, etc etc.