Translation: Make it possible to translate errors, warnings, and other messages

[HenrikBengtsson]

Wish

Add support translation of error and warning messages.

Tasks

1. Update all stop(msg) and warning(msg) calls to use stop(gettext(msg)) and warning(gettext(msg)), or possibly gettextf(fmtstr, ...) and ngettext(n, msg1, msg2)

2. For native code, update all error(msg) to error(_(msg))

3. Create a po/R-{{package-name}}.pot with msgid and msgstr entries

4. Harmonize messages, if possible, to lower the number of unique messages that need translation

5. Ask community for help to translate to other languages

References

The potools package looks like a useful tool, e.g. rstudio::globals(2021) talk on 'Making .pot-ery with R: Translations in R Packages' and upcoming useR! 2021 workshop.