HI, I'm french my english is not very good. But, i want pass my game Don't Starve on steam. I need you. thanks you.

What were you trying to say here?

GOG.com does not offer Steam keys.
I guess your only choice if you really want that game on Steam is to buy it again there.

GOG.com and Steam are competitors. GOG.com isn't likely to give out Steam keys.

Sometimes developers give out Steam keys for games brought on other platforms.

Sorry for the late response, but follow this link: http://support.kleientertainment.com/customer/en/portal/articles/1803621-i-bought-don-t-starve-from-gog-do-i-get-don-t-starve-together-on-steam-

GOG will not provide you with a Steam key. The game company (Klei) will provide you with a Steam key if you bought Don't Starve before June 3rd, 2015, by following the link above and sending them an e-mail.

If you bought Don't Starve more recently (after June 2015), you may not be eligible for a Steam key. But, you can try contacting them anyway to see what they say.