Hi DMehaffy,
Yes, I know that it’s not recommended, shame on me 
I stopped pm2 and run it manually with in development mode using npm run develop.
It still does not work, the error log :
info Installing i18n...
error Error: Command failed: npm run strapi -- install i18n
- Installing dependencies
spawn yarn ENOENT
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! strapi-lfg-institutional@0.1.0 strapi: `strapi "install" "i18n"`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the strapi-lfg-institutional@0.1.0 strapi script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! /home/lfg/.npm/_logs/2021-04-30T07_57_43_140Z-debug.log
> strapi-lfg-institutional@0.1.0 strapi /home/lfg/strapi-lfg-institutional
> strapi "install" "i18n"
at makeError (/home/lfg/strapi-lfg-institutional/node_modules/execa/index.js:174:9)
at /home/lfg/strapi-lfg-institutional/node_modules/execa/index.js:278:16
at processTicksAndRejections (internal/process/task_queues.js:97:5)
at async Object.installPlugin (/home/lfg/strapi-lfg-institutional/node_modules/strapi-admin/controllers/admin.js:50:7)
at async /home/lfg/strapi-lfg-institutional/node_modules/strapi/lib/middlewares/router/utils/routerChecker.js:79:22
at async /home/lfg/strapi-lfg-institutional/node_modules/strapi-utils/lib/policy.js:68:5
at async /home/lfg/strapi-lfg-institutional/node_modules/strapi/lib/middlewares/parser/index.js:48:23
at async /home/lfg/strapi-lfg-institutional/node_modules/strapi/lib/middlewares/xss/index.js:26:9
debug POST /admin/plugins/install (505 ms) 400
Do you have any idea ? 
Thank you for your help