If you run after two hares, you will catch neither.

proverbs with haresMeaning: 

Concentrate on one thing at a time or you will achieve nothing. Trying to do two or more things at a time, when even one on its own needs full effort, means that none of them will be accomplished properly.

Origin:
The saying is attributed to Publilius Syrus in the form of Latin proverb "Duos insequens lepores, neulrum cap it". 

Related Proverbs: 
A bird in the hand is worth two in the bush.
Don't bite off more than you can chew.
Grasp all, lose all.
He who has many irons in the fire, some of them will let burn.
Jack of all trades and master of none.

Alsatian Translation
Wer zwei hase mit'nander will fange, fangt keiner.

M'r kan net zwei Mukke uf's mohl fange.
In English: One can't catch two flies at once.
Contribution by Sylvie Dassiou

Arabic Translation
لا يمكنك مسك تفاحتين بيد واحدة
In English: One can't hold two apples in one hand.
Contribution by Ahmed Abu-Shnein

قل ضرب من يمسك بالحجارة الكبيرة
In English:  He who holds big stones can rarely hit (harm).
Contribution by Baslan Qurashi

Bulgarian translation / превод на български език
От два стола - на земята.
In English: [Sitting] on two chairs [ends in sitting] on the ground!
Contribution by Alexander AlexievДимитър Димитров and Elmira Kotscheva

Catalan translation / traducció al català
Molts oficis, pocs beneficis.
In English: Many professions, few benefits.
Contribution by Esteve Mata López

  • Czech translation / český překlad 
    Kdo chce víc, nemá nic. 
    In English: (The one) Who wants still more ends up with nothing. 
    Contribution by Ivo Jurásek
Danish translation / dansk oversættelse
Den der jager to Harer af een busk, faaer sieden nogen af dem.
In English: If chasing two hares in one bush, you don't get close to any of them.

Dutch translation / Nederlandse vertaling 
Wie op twee hazen tegelijk jaagt, vangt geen van beide.
In English: Who hunts for two hares at once, catches neither.

Op twee paarden wedden.
In English: To bet on two horses.

French translation / traduction français 
A vouloir courir plusieurs lièvres à la fois, on risque de n'en attraper aucun.
In English: Running after more hares at the same time, one risks catching neither.
Contribution by Eric Lesieur

Faire d'une pierre deux coups.
In English: To kill two birds with one stone.
Contribution by Steve Zuccaro

Qui trop embrasse, mal étreint.
Contribution by Fatna Dymling and Steve Zuccaro

Qui veut trop, n'a rien.
In English: Who wants too much, has nothing.
Contribution by Jean van Hanxleden Houwert

Un tien vaut mieux que deux tu l'auras.
Contribution by Monique Provencher

German translation / Deutsch Übersetzung 
"Wer sich zuviel vornimmt, erreicht nichts." oder
"Wer sich zuviel (auf einmal) vornimmt, führt nichts richtig durch."
In English::
"He who performs many things, does not achieve anything",
"He who performs many things (at the same time), does not accomplish anything in a proper way".
Contribution by Elmira Kotscheva 

Man kann nicht auf zwei Hochzeiten tanzen.
In English: You can't dance at two weddings (at the same time).
Contribution by Marinus Vesseur

Gujarati translation 
બે ઘરનો પરોણો ભૂખ્યો મરે.
In English: Guest of two host will starve of hunger.
Pronounced as bay ghar no parono bhukhyo murey. 
Contribution by Timir Tejtimir

Hebrew translation / תרגום עברית
תפסת מרובה, לא תפסת
In English: If you caught many, you caught none.
Contribution by Michael Davison

אי-אפשר לרקוד בשתי חתונות באותו הזמן
In English: You can't dance at two weddings (at the same time). 
Contribution by Michael Davison

תפסת מרובה לא תפסת
In English: If you want to get too much, you will get nothing.
Contribution by Sabine Seleznyov

Hungarian translation /Magyar fordítás
Aki sokat markol, keveset fog.
In English: He who grabs too many things at once, catches less eventually.
Contribution by Klára Kalamár

Két lovat ül meg egyszerre.
In English: Ridding on two horses at the same time. 
Contribution by Imola Korhecz

Két szék közt a pad alá esik.
In English: He who tries to sit on two chairs will end up sitting on neither.
Contribution by Andrea Hudecz

Italian translation / traduzione italiana
Chi due lepri caccia, l'una non piglia e l'altra lascia.

Chi troppo vuole, nulla stringe.
In English: Who wants too much can reach nothing.
Contribution by Ada Prelazzi, Sara Borghi and Marina Busacchi

Prendere due uccelli con una fava.
In English: To kill two birds with one stone.
Contribution by Steve Zuccaro

Irish translation (Gaelic) / aistriúchán Gaeilge
Ní féidir leis an ngobadán an dá thrá a fhreastal.
In English: The sandpiper (a wading bird) cannot attend to two beaches.
Contribution by Padraic de Bhaldraithe

Latin translation / translationem Latinam 
Duos insequens lepores, neulrum capit.
Contribution by Silchenko Victoria

Qui nimis capit, parum stringit.

Latvian translation / latviešu tulkojums
Divus zaķus reizē ķerdams nevienu nenoķersi.
In English: Going after two birds at the same time means catching neither. 

Macedonian translation / македонски превод
 Koj na dve stolici sedi, moze da padne (ili da gi izgubi dvete).
In English: Who is sitting on two chairs, may fall (or to lose them both).
Contribution by Biljana Biljanovska

Persian Translation / ترجمه فارسی
دو تربوز به یک دست گرفته نمی‏شود.
In English: You can't hold two watermelons in one hand.

با یک دست نمی توان چند هندوانه بلند کرد
In English: You cannot carry many watermelons in one hand.
Contribution by Shima T. Jazayeri

Polish translation / tłumaczenie polskie
Kto dwa zajace goni, zadnego nie zlapie.
In English: Who chases two hares, catches neither.

Portuguese translation / tradução em português
Quem duas lebres caça, uma perde, a outra passa.
In English: Who hunts for two hares, loses one (and) passes by the other.

Quem core a duas lebres, não aphana nenhuma.
In English: Who runs for two hares, catches neither.

Quem tudo quer, tudo perde.
In English: Who wants it all, loses everything. / Who wants to catch all, looses all.
Contribution by Ana Baeta Louro

Gato com dois sentidos não pega ratos.  (North of Brasil)
In English: A cat with two senses does not catch any mice.
Contribution by Iandra Silveira

Quem tudo quer, nada terá.
In English: [The one] who wants all, shall have nothing.
Contribution by Carlos A R de Souza

Romanian translation / traducere în română
Cine aleargă după doi iepuri, nu prinde niciunul.
In English: Who runs for two hares, catches neither.
Contribution by Lia Elena Perianu  and  Andreea Visan

Cine doi iepuri gonește, niciunul nu dobândește.
In English: Who chases two hares, catches neither. 

Russian translation / русский перевод
За двумя зайцами погонишься - ни одного не поймаешь!
In English: If you run after two hares, you won't catch a single one.
Contribution by Silchenko VictoriaOlga Apollonova and Mikhail Evstyugov-Babaev

Serbian translation /cрпски превод
Ko traži veće, izgubi iz vreće.
In English: Who looks for something bigger, loses what he has in (his) bag.
Contribution by Nebojša Crnovršanin

Slovene translation / slovenski prevod
Če sediš na dveh stolih naenkrat, boš na koncu pristal na tleh.
In English: If you sit on two chairs at a time, you will finally land on the floor. 
Contribution by Mira Hladnik

Spanish translation / traducción al español 
Corre tras dos liebres y a ninguna alcanzarás!
In English: Run after two hares and you will catch neither!
Contribution by Carlo Tanne

El que mucho abarca, poco aprieta.
Contribution by Olga Vinas and Gabriela Garcia Calderon Orbe

El que quiere matar dos pájaros de un tiro, no mata ninguno.
In English: Who wants to kill two birds in one shot, kills none. 

Quien mucho abarca, poco aprieta.
Contribution by Esteve Mata López and Lita González-Dickey

Quien todo lo quiere, todo lo pierde.
In English: Who wants it all, loses everything.

Swedish translation / svensk översättning
Ha många järn i elden.
In English: Too many irons in the fire. (negative connotation)

Ukrainian translation / Український переклад
За двома зайцями погнатися то й жодного не впіймати.
In English: Who chases two hares, catches neither. 
Contribution by Silchenko Victoria