Could there be some connection between Arabic falaha meaning to till the soil and German pflügen, Pflug or English plough, to plough?
Probably not, at least not provably so. Since Arabic and Germanic aren't related (certainly not at a time depth shallower than the development of agriculture), the words can't be cognate. Could one be a borrowing from the other? Well, English plough has no clear cognates outside of West Germanic, while Arabic falaḥa has cognates in other Semitic languages (e.g. Hebrew p-l-ḥ "to divide, cut asunder"). If there was borrowing, then, it would have to have been either from a Semitic language into West Germanic, or from a West Germanic language into Proto-Semitic. The latter is impossible because Proto-Semitic predates West Germanic by milennia. The former isn't strictly impossible, but these aren't language groups that are known ever to have been in contact, so it is unlikely. One could hypothesize that borrowing occurred through some intermediary language, but that would be highly conjectural and completely unprovable.
this may help, there are many connections(not sure about the german one though, could have been done at the time of the crusades?), as we have been traditionally taught, the words in the Quraan rooted from the Arabic/Semitic Fa-La-Ha, i dont know its dual-roots, but here is a site i found with many reference most seem legit and accepted by Arabic scholars as well as Muslims scholars http://www.memidex.com/fellahin, anyways the connection to success is a bit obvious if you understand Islamic or Arab philosophy or even Sufism. Tilling the land for farming is how we use it, but farming takes steps stages, so example Allah has used it in Quraan Chapter 23 Verse 21 word No2 as aflaḥa, its a Verb in 3rd person masculine by gender singular form IV perfect(past) verb, know in Arabic the morphology is in form 4/IV which tends to means it makes intransitive verbs transitive, and transitive verbs doubly so. a verb is this form has the meaning of, he made himself do or perform an action. A reflexive causative, i.e. he made himself do something transformative to a place or a state. also see http://quran.com/23/1 tick all translations to compare and you'll see the basic idea So i hope this clears up the connection of Success and Farming, basically Fa-la-Ha means to go through a process to achieve in a given field, traditionally farming. so its kind of a root used in context of success, prospering, but it is used when the success is based on a systematic process in the connect above its been used in the past/perfect sense it has been completed it is so. hope this helps