You should do things as correctly as possible, because people looking at your data over 10 years will not understand your storage system.
I don't think all people have an English personal name also, is this something official, in that the writing of the English is actually somewhere registered?
For example, Pei, with chinese name (M prepended assume it's chinese characters) MPei MWong
My take would be:
1/family name: MWong
2/Given name: MPei
3/click on the edit button after the name, to open the name editor. Chinese names are ordered typically Family Name Given Name, so if your standard ordering is different than that (it is set in the preference, eg with a , ), you can set the sort name to what you would expect for chinese (you can create other name formats in the preferences).
4/As these are Chinese characters, and we cannot read them, it might be best to set a group name to the English 'Wong', which will make it easier to find
5/Make sure the type of the name is 'birth name'
6/The romanized name Pei, or full Pei Wong, is the Western Name of the person, or a self-chosen western nick name, you should ask the person. If a nickname, you can write Pei in the Nickname field in the name editor. If it is the Western Name, you should create an alternate name: in the person editor, go to tab Names, and add a new name. Set Given to Pei, and family to Wong or MWong. Set name type to 'Western Name' (you can just type that, and Gramps will store it for further use)
See also http://en.wikipedia.org/wiki/Chinese_name#Alternative_names
for other possible alternative names when dealing with Chinese names.
So for variants in name, use the alternate name tab of the person editor, and you will be able to later search on a name that is registered there, and find the person.
Don't forget to add sources to the names via the name editor.