Updated article: Setting language preferences in a browser

In addition to generally updating the information, the following changes were made:

• rearranged most of the material and rewrote the majority to make it more readable
• updated information about desktop browser settings
• limited that section to just a representative sample of major browsers
• removed ‘Finding and choosing custom tags’, since no longer relevant
• added information about mobile devices

See the updated article.

See the github commit diffs.