Operating system name and version: Debian 9
Version of smsd: latest
Smsd installed from: debian repository
Name and model of a modem / phone: Wavecom
Interface: USB

When I send SMS that contains characters from GSM 3.38 codepage then I'm receiving incorrect data.

PDU that I have received for SMS with EUR symbol.
0791249130330300040C91249150286469000091602202417080046150390C

Text in octets containing 7bit chars : 61 50 39 0C

After decoding, we can see that first letter "a" is correct : 0x61
Second is EUR symbol, so first should be 0x19 ( indicating that next 7bit is pointing to extended charset of GSM 3.38 ) ,
instead, second 7bit char is 0x20, which is SPACE not ESC ( 0x19 ).

So, now I don't know if smstools is manipulating PDU or ....

Thank you for ideas.

Correction 0x1B not 0x19

Smstools is not manipulating incoming PDU in any way ...
I think that also modems should not manipulate PDU's, but you never know...

What is the device or program which was used to send this SMS?

If you send the same SMS with the same device to some handset, is the message shown as expected?

When sending SMS containing a€a from Samsung S6 to smstools, the received PDU is like:
0791535880770153040C9153485011111100009160323240952104E14D390C

The result is correct. In your case I do not know where the ESC was changed to the SPACE.

Sending device was iPhone ( XR, 8 ) and some android based device.
Also tried 3 different GSM providers as senders and 2 different as recipient. Each time the same issue.

SMS between IPhones ( with disabled iMessage ) was sent correctly