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While it seems unlikely that Deligne's article has been translated, there are several alternative sources in English that may be of use, including:

Tate's article *Number-theoretic background* from volume 2 of the Corvalis proceedings. It provides a lot of introductory material on Weil groups (some of it taken from Deligne's paper).

Chapter 7 of Bushnell & Henniart's book *The Local Langlands Conjecture for* GL(2) (Springer-Verlag, 2006, MR2234120). It presents (with proofs) the material on Weil groups and their (Weil–Deligne) representations as well as proving the existence of the "local constants", thus covering a lot of what is in Deligne's article. It even has a proof of the ℓ-adic monodromy theorem previously only available in the appendix to Serre–Tate!

Tate's article Local constants, in *Algebraic number fields*: L-functions and Galois properties (Proc. Sympos., Univ. Durham, Durham, 1975), pp. 89–131. Academic Press, London, 1977.

[Anyone reading this should feel free to add more bibliographic information, further references, or additional commentary on the various suggestions.]

Local constants, inAlgebraic number fields: $L$-functions and Galois properties (Proc. Sympos., Univ. Durham, Durham, 1975), pp. 89–131. Academic Press, London, 1977, might also be of some help. $\endgroup$ – Chandan Singh Dalawat Mar 27 '11 at 6:145more comments