This is a long neglected aspect of the Mandarin lexis.
The naive view holds that Mandarin contains few lexical gaps. Any gaps that may have emerged since late Ch’ing are filled by calques and especially phonetic loans.
Nothing could be further from the linguistic reality.
In most fields of modern learning, serious discussions are held in the lingua franca. This leads to two types of diglossia:
The learned tend to write in a European language even when they keep speaking Mandarin. Ironically, they are the very group for whom loanwords are supposed to be most useful.
The lexical gaps in their conversation are filled by the lingua franca directly rather than by loanwords. This is particularly the case with those who know the Wu dialects, for whom near-native pronunciation for an Indo-European language can be easily achieved in such mixed contexts.
Loanwords, if they get used at all, tend to occur in low registers today.