Veusz can be translated online at https://www.transifex.com/projects/p/veusz/. You can either translate the strings online using the website, or download a ts format file for use with the Qt Linguist application and upload again. If you're interested in translating Veusz, it is recommended to first say so on the list to make sure that effort is not duplicated.

To try out your translation, take the ts format file and convert it to a qm file with

lrelease in.ts -qm out.qm

You can then use the --translation=out.qm option to veusz to load the translation.