These are called "square brackets" in English.
Here are the British Phonetic symbols for the words:
Square brackets: /skweə ˈbrækɪts/
Contextual Example:
Scenario: Discussing how to include optional information in a document.
Dialogue:
Person 1: How should I include the additional data in this report? It's relevant but not essential.
Person 2: You can put it inside square brackets. That way, it indicates that the information is supplementary.
Person 1: Great idea! I'll make sure to use the square brackets to clarify that it's optional.
Square brackets are often used in writing to add explanations, clarify usage, or indicate modifications to direct quotes.