من الممكن القيام بعملية تطويل للحروف كما قمت أنا بهذا الشكل وبهذا نكون احتفظنا بنفس تنسيق المصدر
الـــتـرددات / أو الحـــدود الــمنخفـضــــة إلــــى أبــعد الحــــدود والــمنخفضـــــة للـغــــاية
(وهذه ترجمة مقترحة إذ لا يتوفر السياق الكافي-لكنها الترجمة الأكثر استخدامًا في السياق الطبي)

https://ar.glosbe.com/en/ar/very low frequency
https://ar.glosbe.com/en/ar/very low frequency

Thank you for posting this very important question. It concerns all English-Arabic translators, and it is helpful to have it address on ProZ.com. However, since the question does not concern terminology, it is not a KudoZ question, properly speaking. It should more properly be posted on the Arabic forum. I will provide my advice below to help you, but please keep the forums in mind for future non-terminology questions.

To answer your question, let me ask you a question: How would you render “Seham Mansour” in Arabic? I would imagine that you would render it سهام منصور. I would render it the same way. In rendering it so, we do not and cannot capitalize. More importantly, we make no attempt to substitute another form of typographical emphasis: no boldface, no italics, no underscore, and no color change. I know some people who place proper nouns in parentheses when writing in Arabic, and I know others who use quotation marks, but such usage is non-normative and should be discouraged because parentheses and quotation marks signify intentions unrelated to emphasis.

Here is my point: we do not usually expect the translated text and the source text to be typographically identical. Each language has its own distinctive typographical standards, born of custom and tradition. For example, in the German language, all nouns are capitalized, not only proper nouns. We write “Buch,” not “buch.” On the other hand, in French, we do not capitalize the names of the months of the year or the days of the week. The English “July” is equivalent to the French “juillet.”

Even within the English language itself, the use of capitalization has not always been as uniform as we think of it today. The typographical rules that we currently teach children in elementary school did not always exist. A casual look at texts from different historical periods will show what I mean. As a matter of fact, the rules continue to change even today. The introduction of instant messaging and social media has had a great impact on the rigidity of typographical rules, even outside of instant messaging and social media. Language is far more fluid than we generally think of it.

It is legitimate, however, to ask whether the use of capitalization in words not normally capitalized should be treated differently in translation. The words “extremely low” and “very low” are not normally capitalized in English unless they happen to form a title. The writer capitalized them not because the rules of English require capitalization, but because the writer wished to elevate the expressions to the level of a standardized term. “Extremely Low” in this context does not mean “extremely low” in a general sense, but in a specifically defined sense. Might it not be possible, even advisable, therefore, to use a similar (but not identical) approach in Arabic?

The answer is yes, it is possible. Does that mean it should be done, and if so, how?

Only the translation’s owner can answer this question. If you were translating a non-proprietary text (a text with no privately owned intellectual rights) as your own private venture, you would have the prerogative to decide what you want to do with typography. You have a variety of emphatical options listed above. You can choose whichever suits you if you deem any of them necessary.

I assume, however, that the text you are translating is part of a paid job for a client through a translation agency. If so, then the client/agency will decide for you, but only if you bring the question to their attention. Otherwise, they would not even know that there is an issue.

Clients (and agencies) are notoriously ill-informed about the distinctive customs and traditions of different languages and different alphabetical systems. Many of them do not even know that Arabic is written right to left. (Even when they know, some of them would say Arabic is written backwards!) And yet, the decision is theirs and theirs alone. It is, therefore, your lot to inform them of the issue and to ask them to give you their official guidance as to how to proceed.

The facts they need to know is that the Arabic alphabet has no case distinction, upper or lower. The phrases “Extremely Low” and “Very Low” are capitalized in English for the purpose of elevating them to the level of standardized terms. Boldfacing, italicizing, and underscoring are possible options in Arabic, but not capitalization. The other option is to use no typographical variation.

I would advise that you approach your agency with diplomacy when you present the facts and the question to them. On the one hand, you need to educate them about the topic. On the other hand, beware of appearing to be doing so. When I educate my project managers about the Arabic language or alphabet, I use expressions like “I will be happy to follow whatever instructions you provide me based on these facts, which I am sure you know.” They like that.

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Note added at 1 day 5 hrs (2020-07-05 07:40:44 GMT)
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My explanation above contains a number of textual errors, which I wish to correct here.

In paragraph 1, the second sentence should read, ". . . and it is helpful to have it addressed on ProZ.com." I incorrectly used the active voice when I should have used the passive voice.

In paragraph 5, the first sentence should read, ". . . but because the writer wished to elevate the expressions to the level of standardized terms." I incorrectly used the singular form when I should have used the plural.

Paragraph 10 errors are structural, affecting the entire paragraph. It should read as follows: "The facts they need to know are: (1) that the Arabic alphabet has no case distinction, upper or lower; (2) that the phrases “Extremely Low” and “Very Low” are capitalized in English for the purpose of elevating them to the level of standardized terms; (3) that boldfacing, italicizing, and underscoring are possible options in Arabic, but not capitalization; and (4) that the other option is to use no typographical variation." I used the singular form "is" when I should have used the plural form "are" in the first sentence. I also used periods (full stops) to separate sentences when I should have used semicolons to make the paragraph a cohesive unit.

I apologize for having failed to correct these textual errors before posting my answer.