You can't remove the default language of your installed Firefox version, so it looks you currently have an English locale installed and Italian as a language pack.

I assume that for the Italian language Remove is enabled ?

• https://support.mozilla.org/en-US/kb/choose-display-languages-multilingual-web-pages

It looks you installed the Italian language pack and not the Italian dictionary. This is a misunderstanding we regularly see happen.

Do you have a dictionary installed and selected?

You can see which dictionary is selected if you right-click in a text area and open the Languages sub menu. At least one dictionary should be installed and have a check mark to indicate that it is selected.

• open the "Add Dictionaries" link to install a dictionary if you do not have one.

The spelling checker is enabled if [X] "Check Spelling" in the right-click context menu has a checkmark.

You can enable or disable spell checking globally:

• Options/Preferences -> General: Language and Appearance: "Check your spelling as you type"
• https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker

You can look here for dictionaries:

• https://addons.mozilla.org/firefox/language-tools/

Note that for spell check you need a dictionary. A language pack provides string translations for the user interface.

You can check on the about:config page that layout.spellcheckDefault is set to 1 (multi-line) or 2 (single-line).

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Thank you Cor-el, but the situation is different. 1. I installed and had very well going Firefox in Italian, WITH its dictionary: typing messages with Gmail web-mail I had all words checked with Italian dictionary, underlining in red Italian typos etc.

2.

To show some commands in English I went to Options-Languages and I ADDED English as language.

3. After all screenshots and other needs done, I went again to Options-Languages to REMOVE English (I had seen the button "Remove" -in grey - before...), but after evidence of English, the button 'Remove' was still grey-unactive.

4. After trying for many times : it is not possible AT ALL to get rid of this second language... moreover, it is not possible at all to even set Italian as first language !

5. unfortunately, all methods suggested here are NOT working.

6. I see others have the same problem: is that a BUG ?

7. Addendum: going back and forth, via different commands and clicks, I ONCE had the button "Remove" activated somehow... ; I removed English and restarted Firefox and even the whole PC, but nothing changed...

I still need help: Thank you again everybody !  :)

Does that mean the "Move Down" and "Move Up" buttons aren't working either? You may be able to edit a setting in about:config. Open a new tab, enter about:config in the address bar, accept the risk and find the following setting: intl.accept_languages To edit it, click on the pencil icon to the right of the setting. I have 4 English variants and I can delete and move any of them.