The relative clause in Persian / Farsi and what it means for international auxiliary languages / Oración relativa en idioma persa / farsi

I've had for a while a copy of Modern Persian by John Mace that I go over about 15 minutes a day to 'soften up' Persian to make it that much easier when I finally get around to being able to putting most of my effort into it. I noticed the other day a section about the relative clause, and it's quite a bit simpler than the relative clauses in most IALs that are used (=Esperanto, Ido, Interlingua, Occidental, etc.). Basically there's one relative clause, ke (که), and it's used for everything where you'd find in which, to which, that, in that, and so on. Here are the examples given in the book for how it works. I've also added an Ido translation to the bottom to show how an IAL would work if it were using the same word order and structure as Persian.

Example 1

• The box that I took the money from
• Sandûghî ké man az ân pûl râ gereftam
• Box-that-I-from-it-money-object-I took
• صندوقی که من ازآن پولراگرفتم
• Buxo-ke-me-de-ol-pekunio-n-me prenis
  

Example 2

• The boy that you spoke with
• Pesarî ké shomâ bâ û sohbat kardîd
• Boy-that-you-with-him-speak-you did
• پسری که شما بآاوصحبتکردید
• Puerulo-ke-vu-kun-ilu-konverso-vu facis

Example 3

• The man that I wrote the letter to
• Mardî ké barâ-ye-û man nâmé râ neveshtam
• Man-that-to him-I-letter-object-I wrote
• مردی که برآی اومن نامه رانوشتم
• Viro-ke-ad ilu-me-letro-n-me skribis

The book gives a number of other examples, but makes it clear that this is the only way to make relative clauses in Persian. It would probably offend the sensibilites of people used to using in which, to which and so on, but for a worldlang I could see using Persian as a base for forming relative clauses.

Some more examples of how it might work off the top of my head:

"The coffee that I like" becomes "The coffee ké I like it"
"The country in which there are many immigrants" becomes "The country ké in it are many immigrants"
"I did that which couldn't be done" becomes "I did that ké it couldn't be done"

Really looking forward to when I'll be able to study Persian full-time.