Chinese is more flexible not just because of the number of majority natives who use it in mainland China and the Chinese nations of Taiwan, Hong Kong, Singapore and Macao but it is also used by Japanese.
There is additionally the global Chinese diaspora located far and wide as well as increasingly more global Chinese middle class luxury consumers and holiday makers. London (and Bicester) luxury retail is much dependent on this trade.
The only issue with Chinese is the spoken form as although Mandarin is the standard and most spoken lingua franca uniting standardised form - most Chinese will speak their original mother tongue Chinese dialect as well as Mandarin.
Overseas Chinese tend to speak their own dialect first such as Cantonese and Hakka and may not necessarily speak Mandarin fluently.
However the written form of which there is the traditional full Chinese characters as used by all Chinese (and Japanese) and the mainland Chinese only simplified reduced shorter hand character form. Those who use the traditional full written form can easily understand the simplified but not necessarily the other way round.
The Japanese tend to use Chinese for names and their own two separate Japanese written forms which is a very different written form.
Of the other useful international non European business (rather than tourism) languages - Arabic is useful as it connects so many nations too.
All languages including Latin is more ideal than just English and indeed the level of English in some schools is arguably worst than those in places like the Netherlands for instance!