for adding languages there are two aspects: the language in the instructions which is done on the back end, and the language used on the map client which is done on the front end. If you want to add Thai as a language, you can follow the instructions at our wiki page for the backend.
@amandus - do you have information for the front end?
As for the OSM map, this is down to OSM itself and I do not believe that you can change the language that is displayed - it always shows the language of the country that you are looking at. For routing though, you can still use the Latin alphabet in the start and end points for defining an address.
For the interface language there are language files stored here https://github.com/GIScience/openrouteservice-app/tree/master/app/languages
If you are familiar with git you can clone the repository, add a thai language file and do a pull request to the repository.
Alternatively, you can just translate the english file to thai (only translate the values after the colon!) and send it to me by mail -> amandus@openrouteservice.org
I have added the translations for the Thai language today and while I think I have done everything correctly I kindly ask you to double check what I have done.
I was unable to find your translation anywhere
I noticed a new column “Thai” in a google spreadsheet, but no actual translations being added.
This spreadsheet, unfortunately, is a relict of times long gone.
For translations of the backend code (i.e., the routing instructions you get for a routing request), refer to our wiki page , as stated above. It will guide you on the process of creating a pull request for adding a new language.