Mixed direction is the normal case, not the edge case
A regional technical proposal routinely carries Arabic narrative, English standards references, Latin-script product names and Western-Arabic numerals in the same paragraph. Handling that means direction is a property of each run of text, not a setting on the document — and that tables, lists and captions each need their own answer.
A tool that treats Arabic as English with the text reversed will fail on the first table of figures.
Terminology is a governance problem
The same English term rendered three ways across three sections reads as three different commitments to an evaluator. Consistency is not a translator's preference; it is something the organization has to decide once and then hold, which means the approved rendering belongs in the knowledge base beside everything else that gets reused.
Reviewers do not all read the same language
A technical lead may review in Arabic while a commercial approver reviews in English, on the same document, in the same cycle. Comments, statuses and approvals therefore have to be language-independent — attached to the section, not embedded in one language's copy of it.