Learn Dutch: Het innerlijk bepaalt je persoonlijkheid, hè? - The inner character determines your personality, right?

While innerlijk is often an adjective meaning "inner", here it functions as a noun: het innerlijk (the inner character or the inside). In Dutch, it is very common to turn an adjective into a neuter noun by simply putting het in front of it to describe an abstract concept.

Why does bepaalt have two 'a's while the infinitive bepalen has only one?

This is due to Dutch spelling rules for keeping vowel sounds long. In be-pa-len, the 'a' is at the end of a syllable, which automatically makes it a long sound. When we drop the -en to get the stem, the syllable is closed by the 'l'. To keep the 'a' sound long in a closed syllable, we must double it to bepaal. Then we add -t for the "it" form, resulting in bepaalt.

How does the suffix -heid work in persoonlijkheid?

The suffix -heid turns an adjective into an abstract noun, exactly like "-ity" or "-ness" in English. Here, persoonlijk (personal) becomes persoonlijkheid (personality). As a helpful grammar bonus: every single Dutch noun ending in -heid is a de word.

How exactly is hè used at the end of the sentence?

Hè is a very common informal tag used in spoken Dutch. You add it to the end of a statement to ask for agreement or confirmation from the listener, much like saying "..., right?" or "..., isn't it?" in English.