A few simple steps is all that is needed to install these language packs. You have the choice of 2 different methods, either by installing the Locale Switcher extension or by using the instructions to perform a one-time preference change:
Download the language pack .xpi from this page (below). Choose to immediately "install" in the Pale Moon browser (the default when left-clicking), skipping the need to save it first.
Install Pale Moon Locale Switcher from this site.
Click the new globe icon with colored bubbles in your toolbar, and select the language you prefer from the drop-down.
Let the browser restart when asked.
Download the language pack .xpi from this page (below). You may also choose to immediately "install" in the Pale Moon browser (the default when left-clicking), skipping the need to save it first (go to step 3). You do not have to restart Pale Moon yet.
If you downloaded the .xpi first, double-click the .xpi in explorer/other file manager. Confirm that you want to install the .xpi in your browser. This will add the language pack to Pale Moon. You do not have to restart Pale Moon yet.
To actually switch to the new language, you also have to make a configuration change. Go to the advanced configuration editor (type about:config in the address bar and press enter).
Find the setting general.useragent.locale
which is set to "en-US"
by default. Double-click it to change.
Enter the language code for your locale, including region if applicable. E.g.: "fr" if you live in France, "ja" if you live in Japan, "es-MX" if you want Mexican Spanish. Use the same code as the file name of the language pack you downloaded.
Close Pale Moon completely and restart it.
en-US заменить на ru-RU
Взято с http://addons.palemoon.org/language-packs/