Does Tableau support google language library?
Have you had any success with translation? Not sure what your data source is, but an option is to connect to a Google Sheet document that contains the text to be translated and use the GOOGLETRANSLATE() function. You would need to figure out a way to join/blend the data to your data source.
What does the result of the gl_translate function look like?
The error you are seeing is because the output is not a vector containing data of the expected type, in this case a string. Tableau should be able to utilize any library in R as long as the results can be shaped into a vector of INT, REAL, String, or Boolean.
Interested to see the results of this usecase!