Where did this Prague envelope sent to China been inspected?

[XiaoH]

Ask for help----
Where did this Prague envelope sent to China been inspected?
I would like to ask experts, where are the two check stamps on the front of this envelope-a purple German check stamp and a black check stamp, and the red check seal on the back? Which country implements the inspection? Which country is the red check seal from? Is it Iranian? Another question is, what post did this envelope take from Turkey to reach China?

[XiaoH]

Censored mark 2.jpg

[XiaoH]

Censored label .jpg

[XiaoH]

How was this envelope sent from Turkey to China? What is the specific postal route? Will this envelope be returned from Turkey to Germany, sent from Germany to the United States, which was a neutral country at the time, then from the United States to Japan, and finally to Fengtian（Moukden), China?

[GassmannP]

Hello

the red seal and the black mark in Arabian letters look like what I've seen several times from Constantinople / Turkey. The post office "Stamboul" is definitely situated in Constantinople. So the letter must have traveled through Turkey.

Censor mark 1 "Überprüft" ("checked" in German) could be from Prague, used by the Austria-Hungarian censorship, according to K.K. Wolter.

can't help with the route after Turkey.

best regards, Peter

[XiaoH]

Dear Mr. Peter, thank you very much for your enthusiastic reply and detailed answers
Kind regards

XIAO Hong