I can't actually speak English well enough to have an open conversation with someone.
My English isn't really good enough to have a free flowing conversation with someone.
ーI can't actually speak English well enough to have an open conversation with someone.
「実際に誰かとフリートークができるほど英語が話せません」
フリートークは和製英語なので an open conversation のように言うと良いと思います。
ーMy English isn't really good enough to have a free flowing conversation with someone.
「私の英語は誰かとフリートークをするほど上手じゃない」
a free flowing conversation のようにも表現できると思います。
ご参考まで！
カナダ 
