Return the full function translation table.
function_table.RdColumns: fn (English name), description (if available), and one
column per supported locale with the localised function name (NA if
not translated for that locale).
Details
If setup_terminology() hasn't been run, returns a single-column
data frame with just fn.
Examples
head(function_table())
#> fn
#> 1 ABS
#> 2 ABSREF
#> 3 ACCRINT
#> 4 ACCRINTM
#> 5 ACOS
#> 6 ACOSH