Translate the following English sentence to French:
"I should like to thank the numerous speakers who have expressed their thoughts, all of which were extremely useful, and particularly those who spoke in French, although it is not their mother tongue."
Je voudrais remercier les nombreux orateurs qui ont exprimé leurs observations, toutes très utiles, et notamment ceux qui se sont exprimés en français, alors que ce n'est pas leur langue maternelle.