What is the ruling on Arabs learning English?

Learning it is a means. If there is a need for it as
a means of calling people to Allaah, then learning it may be obligatory.
If there is no need to learn it, then do not occupy your time with that
or let it distract you from things which are more important and more
beneficial. People vary with regard to how much they need to learn English.
The Prophet

(peace and blessings of Allaah be upon him) commanded Ibn Thaabit to
learn the language of the Jews. Zayd ibn Thaabit said: “The Messenger
of Allaah

(peace and blessings of Allaah be upon him) commanded me to learn the
language and writing of the Jews for him. He said, ‘By Allaah, I do
not trust a Jew to write my letters for me.’ So I learned it, and no
more than half a month passed by before I had mastered it. I used to
write it for him if he wanted a letter written, and I would read it
for him if a letter was sent to him.” (Narrated by Abu Dawood, Kitaab
al-‘Ilm, Baab Riwaayat Ahl al-Kitaab; Imaam Ahmad, part 5,
p. 186; al-Haakim, al-Mustadrak, part 1, p. 75 – he said it
is a saheeh hadeeth, and al-Dhahabi agreed with him). 

Learning English is one of the means which, if you need
it you may learn it, and if you do not need it then do not waste your
time with it.