Adding a translated version to your scenario is simple and all you need is already implemented in Railworks.

In the launcher window go to the last tab "localisation", search your scenario(s) in the left tree and mark the languages you want it/them translate to in the middle row. Supported languages by default are english, german, russian and spanish, but there are fan made translations for the complete game in much more languages. When you have selected everything click on "Export xls" and save the file somewhere, e.g. your desktop. Open the Excel file with Microsoft Excel or Open Office and add your translated texts in the according columns. When you are done editing save the file and close it. Then go back to the RW launcher window and click the button "Import xls". When you have marked the checkbox "include existing translations" you will be asked if you want to overwrite existing translations, answer it with yes and it will present you a lot of errors with "duplicate string ID", which is okay. Railworks will now create .lan files for all languages that are included in your Excel file and you can also make new texts for your original language when you import them. A new .lan file will be created and if that is present, RW will always load texts from it, regardless if they are present in the scenario's .bin file or not.