It takes a lot more than a font to preserve a language; people didn't have computer fonts for thousands of years. And for that matter, there are lots of fonts

It takes a lot more than a font to preserve a language; people didn't have computer fonts for thousands of years. And for that matter, there are lots of fonts that work for particular scripts. And a given language is unlikely to mix scripts--they won't, for example, use some Devanagari characters and some Hangul ones. Even if you consider just the need to make the written language available on computers, there are other efforts. SIL is one organization that has developed fonts for minority (including endangered) languages for decades: https://software.sil.org/fonts/ https://software.sil.org/fonts/. They're part of a Christian missionary organization, hence their interest. But they make the fonts freely available to everyone, indeed their license is commonly used for free fonts. Besides fonts, if you want to use a language on a computer, you probably need a keyboard mapper. For languages for which a standard keyboard hasn't been developed, Keyman (https://keyman.com https://keyman.com) is often used. And of course there's the need to develop a writing system--a mapping from sound to characters--in the first place, a task which has not yet been done for many languages, and which is far from trivial for most languages. The linguistic study called phonology is a first step in developing an orthography. And then you have to train people to use the orthography; writing does't come automatically.