That was not the problem. I added execution rights (chmod +x) to all libraries inside /usr/share/textsuggest/libs/, now the server went further and says:
textsuggest-server: symbol lookup error: /lib/x86_64-linux-gnu/librt.so.1: undefined symbol: __clock_nanosleep, version GLIBC_PRIVATE
I suppose that my version of librt.so isn't appropriate for it.