A quick and dirty workaround: create a softlink to the existing language file:

Example: Your phone is set to Spanish. Use the English texts

ln -s /usr/share/locale/en/LC_MESSAGES/procalc.mo /usr/share/locale/es/LC_MESSAGES/procalc.mo

A better solution would be to translate the content of the attached file and post it to the author. There are only a few words to translate