Western grammatical influence on vernacular Chinese in the 20th century
Regarding to how early writers are influenced by western languages. The renowned poet and translator 余光中 has written quite a lot about it. Below are some examples he mentioned in his articles.

Deliberate plurals. Traditionally plurals are only used when absolutely necessary. In the following sentence the reader doesn't actually care whether it's one fly, a group of flies, or fly as a species. Therefore, it's better to leave it out. 


  战士战死了的时候，苍蝇们所首先发现的是他的缺点和伤痕…… ——鲁迅《战士和苍蝇》


Deliberate plurals, and apparent western pronoun-phrase -- "your total extinction". A colloquial way to say it is 我诅咒你们全灭.


  大小一切的苍蝇们……我诅咒你的全灭。——周作人《苍蝇》


Yes we know you've been to Cambridge. We can totally tell. "不曾知道过" is an imitation of the English past participate "haven't known". "更大的愉快" is an imitation of the English comparative "greater happiness". In whole it looks like an awkward English sentence being translated to awkward Chinese. 我不知道什么比这更愉快 would be much better.


  我不曾知道过更大的愉快。——徐志摩《我所知道的康桥》


Typical stacked modifiers. Very unsinological I'd say. It's not even good English. With English you can use clauses to right-branch a sentence, with modifiers trailing behind, theoretically ad infinitum. With Chinese, all modifiers are supposed to put at the left side. If the modifiers gets overabundant, the sentence would be very hard to digest. Usually this kind of sentences should be completely restructured.


  我这本书只预备给一些“本身已离开了学校，或始终就无从接近学校，还认识
  些中国文字，置身于文学理论、文学批评以及说谎造谣消息所达不到的那种职务上，
  在那个社会里生活，而且极关心全个民族在空间与时间下所有的好处与坏处”的人
  去看。——沈从文《边城》


Another example of stacked modifiers.


  但我是更感动于那些无望的度着寂寂的光影，沉默的，在憔悴的朱唇边浮着微笑，属于过去时代的少女的。——何其芳《哀歌》


余光中 went on to say that some of the writers, including 鲁迅 and 胡适, are already excellent 文言文 writers, but when they write 白话文, they tend to lose themselves and incorporate western language features into their articles. 鲁迅 even did this deliberately because he thought the contemporary Chinese wasn't expressive enough and it had to be improved this way.

At first this was only a literary vernacular, but they do pierce into the spoken language. Modern mandarin is already a conglomerate because of the influence of early 白话文 and their authors. In late 1970s 余光中 even proposed to eradicate 恶性西化 in Chinese.