Did you have any luck with this filter approach? I have exactly the same problem. The 255 character limits hits me on page titles, on only the 3rd language for a site I am building, and the long term plan is to have the site in 6 languages. So your situation is not unique. In fact I see many international sites that display in 5 or 6 languages.
I was also thinking of manually changing the database field size, but it looks like from your post 3 years ago, that also involved changing the code in many places, which will break with each Moodle update, so that is not viable.
I looked at the Generico filter demo video, and it mentions that it is limited to 10 filters. That rules it out in my situation. I am translating not one course, but dozens, so there would be hundreds of filters needed.
The only solution I am seeing is to use the restrict access by language filter. So what this means is that rather than using the multi-lang span filter, I would have to create a separate page / activity / file for each language, and then restrict access to each so that they display only if the appropriate language is chosen by the user.
I'd appreciate any insights from your testing.