If I had to guess, I might think that this is the only version that has existed

The changelog shows that there have been versions from 0.01 through 0.10, the most recent release being May 2017.

In Makefile.PL , should I just go: PREREQ_PM => { WWW::Google::Translate => '.1', },

I would recommend against reformatting the version number like that, as it might potentially confuse the tools that do version number comparison. Either specify '0' for "any version", or '0.10' for that version.

Since users will need to install this module from CPAN anyway, and in particular because it's a pure-Perl module without any exotic dependencies, I think it's probably fine to require a version of the module version that's ~2 years old.