* Definition of "written" is fuzzy: Some languages have only recently developed writing systems, while others have complex, evolving ones. Does a language with limited script use count as "written"? What about languages with multiple writing systems?
* No definitive list: There's no universally agreed-upon list of all languages, let alone which ones are written. Many languages are spoken by small groups and haven't been formally documented.
* Languages are constantly changing: New languages emerge, some die out, and others evolve, making a static count difficult.
However, we can make some estimates:
* Number of languages: Ethnologue, a widely used resource, estimates around 7,151 languages spoken worldwide.
* Languages with writing systems: It's likely that a significant portion of these languages have some form of writing system, even if it's not widespread or used for all purposes. Estimates suggest around 4,000 languages may have a writing system, but this is still very approximate.
In conclusion: While we can't be precise, it's safe to say that thousands of languages worldwide have some form of writing system.