ggplot call changes locale LC_NUMERIC variable - r

Question

I am struggling with a strange behaviour of R/ggplot.
Starting a fresh R session and calling sessionInfo() gives
R version 3.5.1 (2018-07-02) Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Linux Mint 19
Matrix products: default BLAS:
/home/nicolai/anaconda3/lib/R/lib/libRblas.so LAPACK:
/home/nicolai/anaconda3/lib/R/lib/libRlapack.so
locale: [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
LC_MONETARY=de_DE.UTF-8 [6] LC_MESSAGES=en_US.UTF-8
LC_PAPER=de_DE.UTF-8 LC_NAME=C LC_ADDRESS=C
LC_TELEPHONE=C [11] LC_MEASUREMENT=de_DE.UTF-8
LC_IDENTIFICATION=C
attached base packages: [1] stats graphics grDevices utils
datasets methods base
other attached packages: [1] RevoUtils_11.0.1 RevoUtilsMath_11.0.0
loaded via a namespace (and not attached): [1] Rcpp_0.12.18
assertthat_0.2.0 dplyr_0.7.6 crayon_1.3.4 R6_2.2.2
grid_3.5.1 plyr_1.8.4 gtable_0.2.0 [9] magrittr_1.5
scales_0.5.0 ggplot2_3.0.0 pillar_1.3.0 rlang_0.2.1
lazyeval_0.2.1 rstudioapi_0.7 bindrcpp_0.2.2 [17] tools_3.5.1
glue_1.3.0 purrr_0.2.5 munsell_0.5.0 yaml_2.2.0
compiler_3.5.1 pkgconfig_2.0.1 colorspace_1.3-2 [25]
tidyselect_0.2.4 bindr_0.1.1 tibble_1.4.2
Notice how LC_NUMERIC is set to C.
Typing 1.2 returns
1.2
After calling the following two lines of code
library(ggplot2)
ggplot(data.frame(a=1:5, b=1:5), aes(a, b)) + geom_point()
My R-session mysteriously changes the decimal separator from a dot to a comma. Typing 1.2 returns
1,2
All plots I generate have the comma as the decimal separator. Calling sessionInfo() returns
R version 3.5.1 (2018-07-02) Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Linux Mint 19
Matrix products: default BLAS:
/home/nicolai/anaconda3/lib/R/lib/libRblas.so LAPACK:
/home/nicolai/anaconda3/lib/R/lib/libRlapack.so
locale: [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=de_DE.UTF-8
LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8 [5]
LC_MONETARY=de_DE.UTF-8 LC_MESSAGES=en_US.UTF-8
LC_PAPER=de_DE.UTF-8 LC_NAME=de_DE.UTF-8 [9]
LC_ADDRESS=de_DE.UTF-8 LC_TELEPHONE=de_DE.UTF-8
LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=de_DE.UTF-8
attached base packages: [1] stats graphics grDevices utils
datasets methods base
other attached packages: [1] ggplot2_3.0.0 RevoUtils_11.0.1
RevoUtilsMath_11.0.0
loaded via a namespace (and not attached): [1] Rcpp_0.12.18
rstudioapi_0.7 bindr_0.1.1 magrittr_1.5 tidyselect_0.2.4
munsell_0.5.0 colorspace_1.3-2 R6_2.2.2 [9] rlang_0.2.1
plyr_1.8.4 dplyr_0.7.6 tools_3.5.1 grid_3.5.1
gtable_0.2.0 withr_2.1.2 yaml_2.2.0 [17] lazyeval_0.2.1
assertthat_0.2.0 tibble_1.4.2 crayon_1.3.4 bindrcpp_0.2.2
purrr_0.2.5 glue_1.3.0 labeling_0.3 [25] compiler_3.5.1
pillar_1.3.0 scales_0.5.0 pkgconfig_2.0.1
Notice how the LC_NUMERIC value has changed. I assume this causes the change in the decimal separator, but I have no idea how that makes sense.
This is something that happened after installing a fresh Mint version together with a fresh, up-to-date R version.
Does someone have an idea of what could cause this?