English is more popular in Vietnam or most of restaurants have English menu so you can order food. People in local markets may not know well English but it is easy to order if you can show them a picture of what you want to buy.
The language of Vietnam is Tieng Viet.
In tourist areas of Hanoi and Hoi An you will find people will speak limited English enough to be able to serve you food and drinks and sell you clothes or souvenirs. Those bookung tours etc will have a higher degree of English due to their job requiring a higher understanding of English. French tends to be more limited to people who may have got their education in France and the very elderly who were alive during colonial times. You may find French spoken in a French restaurant in Hanoi but less likely in Hoi An.
Thank you all for your help.
English education is a major industry in VN and all of Indochina - the young are especially eager to use English.
It's a good idea to learn some basic words and phrases in Vietnamese. (Plenty of videos on YouTube). It will get you plenty of respect from locals for having the courtesy to have a go.
If they don't know english you can try on your phone. use google translate from english to vietnamese. i sure it will help.
Restaurants' staffs speak English well (maybe it's requirement for applying for customer service job)
In local markets, English communication is limited. Maybe you ask locals who are fluent in English go with you. University students are open and happy to show you their cities
You can úe english in a big restaurant but the small one or far from the center the staff speak Vietnamese only.