Hi!! I will try to explain you the easiest way to download BO4 in your preferer language.
First of all you need to download the files from Step 2 of the guide.
Before continue to the step 3, you need to open the .bat file into an editor like Notepad, Notepad++, VSCode, etc. and then you will edit this line:
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Where it says "--lang enUS" you can introduce the lanaguage as your choice following the language ISO standard logic:
Lowercase letters: represent the country language itself: en, es, pt, de, etc.
Uppercase letters: represent the country region/zone. You can try using the country or continent abbreviation: ES, US, EU, PT, DE, etc.
PD: Sorry if I can't explain it well in english. If someone has some doubts about this method, contact me and I can explain it in spanish.