In reality, it's not. Foreigners here are mainly Eu and North America, countries that are prejudiced against China. Buying parts from them is like buying someone's noose to hang yourself. And the West can use any excuse to block supply if the two sides come into conflict, or they simply want to destroy China, the same way they nearly brought ZTE to bankruptcy and got Huawei in trouble.
Instead of buying parts from the West in the hope that the West will accept the C-919, China should manufacture 100% of the components domestically, then perfect the C-919 to meet international standards. Foreign approval or not, is not so important.
There is a reason why China is using so many Western companies. (Among others) Its because these companies are working on their specialised industry sub-fields for many decades and have created their own "world-class" management system for manufacturing, QA, engineering processes etc.
A company doesn't just create a new thing out of thin air. Necessary processes and procedures must be in place to create and engineer new products.
I am guessing that the Chinese suppliers can create working (but not world class) products, however their internal processes are not mature enough to ensure a 100% reliability.
I mean this is the commercial aircraft business. We are talking about millions of people flying safely. Even a slight reliability issue could be devastating for the industry.
So, it is good that China is developing their plane step by step. First use foreign supplier to get experience (processes, manufacturing, QA etc) and after 5-10 years start replacing them with the (now) domestic replacements