3.1.2 Language of Parts (AA) mainly applies if there are passages in the learning content that are different from the main language. This is especially useful in language courses so that screen readers can pronounce the different language sections correctly. However, this is a less supported capability, so check if your authoring tool allows you to do that.
3.1.3 Unusual Words (Level AAA) is about having a mechanism in place for unusual words such as idioms or jargons. These are especially hard to understand for non-native speakers or people with cognitive disabilities. Having a “mechanism” might mean that the meaning is explained in brackets, in a footnote, by a link to the definition, or are simply left out.
3.1.4 Abbreviations (Level AAA) is about making sure that there’s a mechanism in place for acronyms and abbreviations. For example, JAWS is an acronym for a speech reader software, but learners might get confused, especially if they don’t see that it’s written in capital letters. The “mechanism” could simply mean putting the full phrase in brackets, (eg: JAWS (Job Access With Speech)), or using a footnote, or adding a link to the definition.
Most learning content creators already know that they should write at a 14-year old’s level. 3.1.5 Reading Level (Level AAA) requires that if the language of the content is too advanced for someone with 7-9 years of education, you provide a version that is understandable for them.
Finally, 3.1.6 Pronunciation (Level AAA) mainly applies if the meaning of content could be unclear or confusing unless the pronunciation of certain words is known. For example, the sentence “She gave a bow, and left” makes sense, but “I saw her bow” can mean “I saw her inclining her head” or “I saw her ribbon or even her tool to shoot arrows”. While the best option may be to avoid ambiguity, if that happens, you can add a phonetic guide after the word (eg: I saw her bow (/baʊ/)), or add a link to the correct pronunciation.