You have to change the following lines in the following files in the qa-include directory:
qa-lang-admin.php: 'categories_introduction' => 'To get started with categories, click the \'Add Category\' button.',
qa-lang-admin.php: 'categories_not_shown' => 'Some questions have categories which will not be displayed.',
qa-lang-admin.php: 'categories_title' => 'Categories',
qa-lang-admin.php: 'categories' => 'Categories',
qa-lang-admin.php: 'category_no_add_subs_x' => 'This category cannot have sub-categories because it is already ^ levels down.',
qa-lang-admin.php: 'category_subs' => 'Sub-categories:',
qa-lang-admin.php: 'recalc_categories_backpaths' => 'Recalculating URL paths for ^1 of ^2 categories...',
qa-lang-admin.php: 'recalc_categories_complete' => 'All categories were successfully recalculated.',
qa-lang-admin.php: 'recalc_categories_note' => ' - for post categories and category counts',
qa-lang-admin.php: 'recalc_categories_recounting' => 'Recounting questions for ^1 of ^2 categories...',
qa-lang-admin.php: 'recalc_categories_updated' => 'Recalculated for ^1 of ^2 posts...',
qa-lang-admin.php: 'recalc_categories' => 'Recalculate categories',
qa-lang-admin.php: 'tags_and_categories' => 'Tags and Categories',
qa-lang-main.php: 'all_categories' => 'All categories',
qa-lang-main.php: 'nav_categories' => 'Categories',
qa-lang-main.php: 'no_categories_found' => 'No categories found',
qa-lang-misc.php: 'browse_categories' => 'Browse categories',
qa-lang-options.php: 'place_side_below_categories' => 'Side panel - Below categories',
qa-lang-options.php: 'tags_or_categories' => 'Classify questions using:',
