Instead of trying to pluralize "heritage," you could:
* Use a phrase like "multiple heritages" or "different heritages" to specify different aspects of heritage.
* Use the plural form of a related noun: For example, instead of "heritages," you could say "traditions," "cultures," or "histories."
For example:
* Instead of "The museum showcases many heritages," you could say "The museum showcases multiple heritages from different cultures."
* Instead of "They studied the heritages of the region," you could say "They studied the traditions and histories of the region."