Now, also the water meter talks to me. Wasserzaehler (Note the thin grey cable, thats the M-Bus cable.) And, after a small modification of the circuit I can talk to water meter and electric power meter connected in parallel to the master.
laser-drucker_005120 IC2 was already added in the last step, since the output of the analog circuit and the requirements of the MCU didnt match concerning their logical polarity. Now, T3 (BS108) and R9 (2k2) have been added to disable the receive path while data is transmitted.
Responding the REQ_UD2 command, the water meter sends this telegram (address 0x30 has been assigned to it first): so 10 5b 30 8b 16 success SO RESP: 68 46 46 68 08 30 72 45 71 43 00 24 23 25 07 02 00 00 00 0C 13 51 84 00 00 8C 10 13 00 00 00 00 0B 3B 00 00 00 0B 26 62 06 00 02 5A CC 00 04 6D 17 16 A9 19 7C 13 00 00 00 00 FC 10 13 00 00 00 00 72 6C 00 00 42 EC 7E BF 1C 35 16 A closer look, consulting the M-Bus documentation reveals the meaning: [table]Octet(s), Field, Meaning 68 46 46 68, Preamble with length, 08, C field, 30, A field (address), 72, CI field, variable data response 45 71 43 00, Ident. No., 24 23, Manufacturer , HYD = Hydrometer GmbH 25, Version, 07, Medium, Water 02, Access No., 00, Status, 00 00, Signature, 0C, DIF, 8 digit BCD 13, VIF, Volume; 10^(3-6)m^3 51 84 00 00, Value, 8.451m^3 8C, DIF, ext; 8 digit BCD 10, DIFE, minimum value 13, VIF, Volume; 10^(3-6)m^3 00 00 00 00, Value, 0 0B, DIF, 6 digit BCD 3B, VIF, Volume flow; 10^(3-6)m^3/h 00 00 00, Value, 0 0B, DIF, 6 digit BCD 26, VIF, Operating time; hours 62 06 00, Value, 662h = 27.6d 02, DIF, 16bit integer 5A, VIF, Flow Temperature; 10^(2-3)°C CC 00, Value, 20.4°C 04, DIF, 32bit integer 6D, VIF, Time Point; time&date 17 16 A9 19, Value, 7C, DIF, LSB; value during error state; 8 digit BCD 13, VIF, Volume; 10^(3-6)m^3 00 00 00 00, Value, 0 FC, DIF, ext; LSB; value during error state; 8 digit BCD 10, DIFE, tariff 1 13, VIF, Volume; 10^(3-6)m^3 00 00 00 00, Value, 0 72, DIF, LSB; value during error state; 16bit integer 6C, VIF, Time Point; date 00 00, Value, 0 42, DIF, LSB; 16bit integer EC, VIF, ext; Time Point; date 7E, VIFE, ?? BF 1C, Value, 35, Checksum, 16, Stopbyte, [/table] Decoding of the time&date type is done like this: 
    if (t_data)
    {
        if (t_data_size == 4) // Type F = Compound CP32: Date and Time
        {
            if ((t_data[0] & 0x80) == 0) // Time valid ?
            {
                t->tm_min = t_data[0] & 0x3F;
                t->tm_hour = t_data[1] & 0x1F;
                t->tm_mday = t_data[2] & 0x1F;
                t->tm_mon = (t_data[3] & 0x0F) - 1;
                t->tm_year = ((t_data[2] & 0xE0) >> 5) |
                              ((t_data[3] & 0xF0) >> 1);
                t->tm_isdst = (t_data[1] & 0x80) ? 1 : 0; // day saving time
            }
        }
        else if (t_data_size == 2) // Type G: Compound CP16: Date
        {
            t->tm_mday = t_data[0] & 0x1F;
            t->tm_mon = (t_data[1] & 0x0F) - 1;
            t->tm_year = ((t_data[0] & 0xE0) >> 5) |
                         ((t_data[1] & 0xF0) >> 1);
        }
    }
(Found on github in the libmbus repo.)