fullcalendar header locale language not changing on angular

I am working in a project using angular 8 and fullcalendar component. My problem is that when the locale changes the header buttons remain in English.

My html:

<full-calendar defaultView="dayGridMonth" [plugins]="calendarPlugins" [events]="displayedEvents" locale="fr"
      [header]="{
      right: 'prev,next today',
      center: 'title',
      left: 'dayGridMonth,dayGridWeek,dayGridDay'
      }">
</full-calendar>

The .ts file is a little complicated to post but I've read here and in their docs that I need to import the locale-all.js file but that does not work. In either case I get this error

Could not find a declaration file for module '@fullcalendar/core/locales-all.js'. 'node_modules/@fullcalendar/core/locales-all.js' implicitly has an 'any' type.

The file exists but it seems that the compiler searches a .d.ts declaration file.

Thank you