Oman Language is a complicated subject as the country although officially an Arabic language state does have several other native languages. Complicating things, even more, is the importance of non-native languages.
Arabic is Oman’s official language and is taught in government schools. It is a Semitic language and does have similarity to other Semitic languages such as Hebrew.
Written Arabic, as found in newspapers, is a standard script and grammar throughout the Arab world as, importantly, it is the script of the Quran. However given the vast area covered by Arabic and until recently the lack of communication between areas such as Morocco and Oman there are innumerable spoken dialects, that may be almost incomprehensible to each other. Oman’s Arabic is considered to be ‘Gulf Arabic’ and is a distinct variation of that. There are some distinct dialects within Omani Arabic.
From Dhofar in the south there are 2 or 3 separate Semitic languages that as a group are called Modern South Arabian. They are Bathari (almost extinct now) Mehri and Shahari/Jebali and today they do not have a script, though it is likely they did in the past. Harasusi, which to my layman’s ear sounds a mix Bedu Arabic with some loanwords from Modern South Arabian, is remarkably classified by academics as Modern South Arabian.
In Musandam, there are two languages Shahi and Khamzari which are creole languages mainly from Arabic and Persian with some Portuguese and English.
Widely spread through northern Oman are two other languages that are spoken by the native population. Swahili, the language of East Africa is used by Omanis whose families lived in or had connections with East Africa. Baluchi a language from Baluchistan, the area spread in the border areas of Afghanistan, Iran and Pakistan is used by Omanis whose families lived in or had connections with those areas.
The major non-native languages in Oman are Bengali, English, Gujarati (from north-west India), Hindu, Malayalam (from south-west India) Tamil (from south-east India and Sri-Lanka), Urdu, and to a much lesser extent Filipino.
It is fair to say that in most places English will be understood.