apply( compiler ) {
		compiler.hooks.compilation.tap( "i18n-coverage", compilation => {
			// don't emit any files
			compiler.hooks.shouldEmit.tap( "i18n-coverage", () => false );
			// find translation keys in JS and HBS files and get locale data from YML files
			compilation.hooks.succeedModule.tap( "i18n-coverage", this._onModule.bind( this ) );
		});

		compiler.hooks.done.tap( "i18n-coverage", this._onDone.bind( this ) );
	}
@type {Map<string, Array<{params: string[], htmlSafe: boolean}>>>}