improve french translations

• see prior art here: !137 (closed)

current english strings here:

• commands: https://0xacab.org/team-friendo/signalboost/-/blob/master/app/services/dispatcher/strings/commands/EN.js
• messages: https://0xacab.org/team-friendo/signalboost/-/blob/master/app/services/dispatcher/strings/messages/EN.js

current french translations here:

• commands: https://0xacab.org/team-friendo/signalboost/-/blob/master/app/services/dispatcher/strings/commands/FR.js
• messages: https://0xacab.org/team-friendo/signalboost/-/blob/master/app/services/dispatcher/strings/messages/FR.js