You could make a translation vector as in the following code. I am not sure all of my translations are correct!
weekdays<-c("Monday", "Tuesday","zondag","viernes", "Friday","lunes","dinsdag", "domingo" )
Animal<-c("Lion","Cat", "Dog", "Horse", "Bird", "Snake", "Giraf", "Mouse")
Visit_number<-c(5,6,2,0,3,8,6,1)
mydata<-data.frame(Animal, weekdays,Visit_number, stringsAsFactors = FALSE)
TranslVec <- c(Monday = "Monday", Tuesday = "Tuesday", zondag = "Sunday", viernes = "Friday",
Friday = "Friday", lunes = "Monday", dinsdag = "Tuesday", domingo = "Sunday")
mydata$EnglishWeekday <- TranslVec[mydata$weekdays]
mydata
Animal weekdays Visit_number EnglishWeekday
1 Lion Monday 5 Monday
2 Cat Tuesday 6 Tuesday
3 Dog zondag 2 Sunday
4 Horse viernes 0 Friday
5 Bird Friday 3 Friday
6 Snake lunes 8 Monday
7 Giraf dinsdag 6 Tuesday
8 Mouse domingo 1 Sunday