OK for the PhpMyAdmin screenshot, i didn’t pay attention enough…
After putting a trach in the Sql.php module, I notice that data seems to be send OK, so conversion is inner.
But this problem occurs ONLY with Projeqtor: all other installed or developped applications runs fine… included PhpMyAdmin.
So there is a major difference between, on the one hand, the non-object mysqli functions in my applications and the PMA object of PhpMyAdmin, and on the other hand, your sql object in Projeqtor.
What is your mysql library ?
For info, environment variables related to character set for the Projeqtor database are :
character_set_client = utf8
character_set_connection = utf8
character_set_database = utf8
character_set_filesystem = binary
character_set_results = utf8
character_set_server = utf8
character_set_system = utf8
character_sets_dir = /usr/share/mysql/charsets/
collation_connection = utf8_general_ci
collation_database = utf8_general_ci
collation_server = utf8_general_ci
According with all I found on the web, that's OK.
The only difference with all other databases is for these "collation database = utf8_unicode_ci", but this is also good and very, very edge effect possible. Actuel problem not concerned.
All services restarted, Projector reinstalled from zero… nothing has changed. All runs fine… except Projeqtor.
Note: to see real storage, open database file with an hexadecimal editor or viewer.

(But I defined InnoDb to have separate tables, better for safety and easier to examinate)