My comment above is a little bit messed up but basically the problem are old translations containing wrong file paths.
WORKAROUND:
Download current translations from Launchpad in .mo-format and replace /usr/share/locale/YOUR-LANGUAGE-CODE/LC_MESSAGES/indicator-weather.mo with the downloaded file (you need to rename the file after downloading).
After restarting Weather Indicator all translations should be shown as expected.
My comment above is a little bit messed up but basically the problem are old translations containing wrong file paths.
WORKAROUND:
Download current translations from Launchpad in .mo-format and replace /usr/share/ locale/ YOUR-LANGUAGE- CODE/LC_ MESSAGES/ indicator- weather. mo with the downloaded file (you need to rename the file after downloading).
After restarting Weather Indicator all translations should be shown as expected.