While translating you can add important, recurring terms to the glossary, the so-called Term base. You can do this by selecting a term in the English source text or your translation and then clicking the "Add term" button in the quick access toolbar (or by clicking "Alt + T").
A new window will open up at the bottom where you can add the corresponding translation and optionally include additional information such as whether the term is case-sensitive, preferred or forbidden. Then click "Add".
Alternatively, you can add terms by going to "Term bases" in the left-hand navigation and then selecting the glossary for your language.
Next, click on "New" to add an English term and the equivalent translation in your language. Then click "Add".