Thinking about this what you are wanting is what amounts to a one way chat application. Someone is typing into a chat window and what they type is displayed on the LED displays.
What the LED display will display will depend on the software driving the display so the crucial detail would seem to be the need to have a computing device that supports UTF-8 and Unicode with fonts with the necessary symbol set for the language desired.
There are a number of open source chat type systems such as described in 5 open source alternatives to Slack for team chat. The question would be what support any of these have for non-Western languages such as Mandarin or Arabic. Languages such as Mandarin and Japanese have a large symbol set and Arabic is written right to left rather than left to right and there are various kinds of ligatures between symbols.
Or I suppose you could just have a remote session to a full screen word processing application and just type into that and let it scroll up and off the screen? That actually might be the easiest approach as the necessary multi-lingual capabilities should be available and you can change the font size easily.
I would consider using a Raspberry Pi 3 or similar small device to drive the LED displays. The Raspberry Pi has several alternative operating systems with Raspbian, a Linux variant, being the standard default. The Raspberry Pi 3 Model B has built in WiFi, 1 GB of RAM, and an HDMI display output. You could set up a device such as a laptop or even a phone and remote into the Raspberry Pi.