Learn English – discriminate, distinguish, differentiate, and discern

Both "heritage" and "inheritance" refer to things that you get from your parents or ancestors or others you have some association with, after their deaths. "Inheritance", when used literally, refers to money, real estate, or other tangible property. "Heritage" refers to intangible things, like ideals, knowledge, and moral standards.

For example, you might say, "My inheritance from my grandfather included $50,000 and a house in Virginia." But, "Our founding fathers left us a heritage of liberty and justice."

The verb "inherit" can be used for either idea. "I inherited my father's antique car collection." Or, "I inherited my father's love of baseball."

'Yes' can be considered the baseline - I can't think of any context in which using it would be inappropriate. (It might come across as slightly over-formal on some occasions, but more likely no-one would pay attention to it) Any official/formal speech will most likely use 'yes', as will almost all written usage.

'Yeah' is an informal equivalent to 'yes'. In casual conversation you are more likely to hear 'yeah' than 'yes' unless the speakers are making a deliberate effort to be precise with their speech (the reason that 'yes' can potentially sound overly-formal). On the other hand, a written 'yeah' will generally only be used when writing dialogue.

'Yah' would be 'yeah' spoken in a different accent. I would personally associate it either with a non-native speaker (the German accent in particular), or with native speakers who are uneducated/unsophisticated.