TL:DR: our ancestors were not unintelligent, and even calquing “Rachel” with “Rosa” or “Rose” was very specific.
If you actually read:
Let’s start with my my own case: I could have taken “ניקול” or “ניכול” as my Hebrew name when I found out that I’m Jewish. I made a concerted effort to look up what a Hebrew name equivalent to my secular name would be. “נצחיה” was already there. As far as my Hebrew middle or second name:
1) I don’t want to give out my secular middle name to most people for multiple reasons.
2) “מרה-טובה” (good bitterness) describes my life perfectly.
Someone else suggested that I just use “מרתה” (Marta or Martha). I declined that suggestion because:
1) That name does not fit with either of my secular names in any way.
2) I am not a direct descendant of any Marta or Martha, as far as I know, and I did not know that my paternal grandfather’s aunt Sophie Martha Thomas-Brighton (née Trudnak) existed until after my great-grandmother (ז״ל) died. I also did not know that Great-Grandma herself was a daughter of Crypto-Jews until after she died. Because I did not know Great-Grandaunt Sophie personally and am (as far as I know) not in contact with any of her living descendants, I think that I would actually be insulting Great-Grandaunt Sophie’s memory and her side of our family if I use “Marta”.
This isn’t just my view. In Jewish culture, uses and transliterations of names as well as translations of names are actually important. Despite what some might say, many actually tried to keep the Jewish (Hebrew or Hebrew-dialect) and secular (non-Jewish) names as close as possible in some or another form.
Now to “Rachel” “Rachel” (“Ewe”) and “Rosa” (“rose” or “pink”): while the names indeed correlate partly due to the first letter in Latin lettering, they also correlate because Rachel’s life was seen like the life of a rose. Fragile and thorny was Rachel’s life indeed, no matter the sweetness or blossoming in it. After all, even though she was the favorite wife of Jacob, she wanted to die because of competition against Leah and her own infertility (“Give me children lest I die!” we read that she told Ya’akov avinu). When she finally had biological children (as the sons born to Bilhah were put with Bilhah instead of her when Ya’akov had to divide everybody), she died in childbirth and named her second child “בן-אוני”—“son of my sorrow”.
Our ancestors understood how thorny, fragile, and bittersweet Rachel’s life was, even if they could read only Hebrew lettering and not—for example—Latin lettering (all of which—despite their various orthographies—the various Romance languages, the Germanic languages, Slavic languages such as Polish and Slovakian, Balkan languages such as Serbian and Croatian, and Magyar use).
Our ancestors were scattered and often could not even read or write in Hebrew dialects, let alone read and write in the various languages surrounding them in the Exile. Their lack of proficiency in any given language—especially after lack of proficiency was forced by oppressive law—did not equate to a lack of intelligence. Therefore, for instance and as demonstrated, they did not just randomly or cavalierly equate “Rachel” and “Rose”— they understood the correlation between the fragile, thorny, and bittersweet life of a rose and the life of Rachel imeinu—which was fraught with peril, distress, and sorrow even in the joys and suffering in the blessings.