Mimic the syntax of logging to use placeholders in translatable
message.
The main advantage is to be able to fallback on the source term if the
translation can not be formatted properly.
It is very common to have errors in translations with missing
placeholders or badly translated (ie. the source
"%(subject)s" -> "%(sujet)s").
Instead of blocking the execution of the code, fallback on source
string.
Task-id: 1853119
Martin Trigaux
3c3b88f676