in file "xfce4-weather-plugin/panel-plugin/weather-summary.c" there is string "%s on the Beaufort scale)\n" which is not included in .pot file. so translated string still has english words, eg. "Greitis: 3.7 m/s (3 on the Beaufort scale)" part "on the Beaufort scale" is not translatable.
Fixed in http://git.xfce.org/panel-plugins/xfce4-weather-plugin/commit/?id=f28ff30e90bf8a3503ffbd4fb9838bc2bd45f398.