Your league is based on European results. For example Europa League or Champions Leage.
The better your club and other clubs from that country do in Europe the reputation of your club increases as does other clubs from this country. For example say PSG and Lyon both got to the semi finals of Champions League the rating may increase by 0.5-1.0 stars, hypothetically.
As your reputation of your league goes up thus the league rating goes up thus the higher quality of players the leagues teams can attract. I managed to get Portugese League up to 4.5 stars last year.
So mate first and foremost get those European results and hope another club from Ligue 1 do the same.