Could you create a minimal reproduce example (reprex) that shows the problem? There are a lot of things which can thwart character display, and a reprex would help narrow down the list. The forums have a guide to help make reprexes: FAQ: What's a reproducible example (reprex) and how do I do one?.
It doesn't need to be long. A shiny app with a single output that mishandles certain characters would work. My quick example:
library(shiny)
shinyApp(
ui = fluidPage("昨日すき焼きを食べました"),
server = function(input, output) {}
)
This displays correctly when I run it. My session info after running that code:
sessionInfo()
# R version 3.5.1 (2018-07-02)
# Platform: x86_64-w64-mingw32/x64 (64-bit)
# Running under: Windows >= 8 x64 (build 9200)
#
# Matrix products: default
#
# locale:
# [1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252
# [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
# [5] LC_TIME=English_United States.1252
#
# attached base packages:
# [1] stats graphics grDevices utils datasets methods base
#
# other attached packages:
# [1] shiny_1.1.0
#
# loaded via a namespace (and not attached):
# [1] compiler_3.5.1 magrittr_1.5 R6_2.2.2 rsconnect_0.8.8 promises_1.0.1
# [6] later_0.7.2 htmltools_0.3.6 tools_3.5.1 yaml_2.1.19 Rcpp_0.12.17
# [11] jsonlite_1.5 digest_0.6.15 xtable_1.8-2 httpuv_1.4.3 mime_0.5