There appears to be no way of including multiple resource dll's. E.g. one can refer to x.dll and only one x.resources.dll.
Put resource dll's into subdirectories, similar to where they were originally: e.g., .\ja-JP\x.resources.dll; .zh-CHS\x.resources.dll, etc.
Larry Gajdos commented
Never mind! On further investigation, a reference to "x.dll" also includes the localized dll's as well. My mistake!