A historical dictionary may differ from a regular dictionary by holding more than definitions of words. It may include entries on important people, places, events, political parties, and institutions, as well as major political, economic, social, and cultural aspects. These entries can also be cross-referenced within the dictionary.
Other aspects of a historical dictionary include:
To discover dictionaries about an area, you can search by keyword or subject term of "dictionaries" e.g. Japan history dictionaries, or Japan politics government dictionaries that finds, among other results, the Dictionary of the Modern Politics of Japan by Stockwin.
Historical encyclopedias will usually have longer entries than historical dictionaries that may include expansive essays. They can range across all areas within a time period such as information on the archaeology and prehistory, the politics and culture, economics, institutions and organizations, wars and conflicts, and religions.
To discover encyclopedias about an area, you can search by keyword or subject term of "encyclopedias" e.g. "southeast asia" and "encyclopedia" will find Southeast Asia: a historical encyclopedia from Angkor Wat to East Timor.
Please note that not all encyclopedias will have these terms. Some may only have the subject term of "history" such as The Cambridge history of Japan. Also, when searching for encyclopedias to keep your keywords broad.