No reason you couldn't begin the process by volunteering and putting your English skills to work--writing articles and press releases, editing newsletters and papers, etc. This will gain you a journyman's knowledge of the organization's issues and internal workings of 501(c)(3) entity, as well as build your all-important professional network. If there's no local environmental organization to volunteer with, pick a community based organization whose mission is of interest. There will me more similarities than differences and you'll be gaining applicable experience.
Ultimately you'd benefit from working technical knowledge (exactly which ones will vary depending on the organization and the environmental area in which you'd like to work). Wildlife, water policy, land use, conservation, sustainable development, recreation...many are science-based, but others focus on law, politics and policy.
A fast track avenue is via grant writing and fund raising. If you develop skills and a track record here, you can get on board pretty much anywhere.
I've worked in environmental engineering but that's a whole other kettle of contaminated fish.