I've been working for more than 15 years in international contexts (Aircraft simulators for QANTAS, Mechanical Engineering support for ITER since 2009). My written English is not so bad (in doubt I use some support from translators) but I need to focus my improvement on my accent and my understanding. Indeed, I attend a lot of meetings where Chinese people, Korean people, Indian people and some other nationalities (American rude accent guys for instance) intervene and sometimes I don't catch everything.
And when I talk to non native English it happens sometimes I have the feeling they don't understand everything while I believe speaking proper English... so I guess it comes from my accent.
Thank you for your support mainly in those points