Jenni did not deal with the specifics of my question and has only given a linguistic theory to support his opinion.
False. He cited an empirical observation to support his analysis, to wit: "Lamed has in classical Hebrew some 360 occurrences of general orientations radiating from the subject ("nach oben" / "nach unten" etc., but not connected with free localities like towns or countries), and all of them in directional sense ("wohin?", to where?) and never purely static-local ("wo?", where?)." Jenni's volume cites the specific examples. This directly, unequivocably answers the central question you posed him: "Therefore, from all of your published comments are you saying that it is highly improbable if not impossible, for 'le' has the local or spatial sense in Jer. 29:10 for this is what is being claimed as your position in agreement with Modern Hebrew scholars?". How could you possibly say that Jenni did not deal with the specifics of your question? In fact, he went on to mention other matters you brought up, such as the rendering in the Vulgate and the KJV.
The facts are that Lexicography allows for a locative meaning and so does the textual tradition beginning with the LXX.
(1) This canard has been addressed time and again in the other thread; I don't know how many times that Narkissos and I told you that the semantic value of lamed depends greatly on the kind of grammatical construction it occurs in. Picking a favorite reading merely on the basis of what "lexicography permits" irrespective of construction is like saying the phrase "running up a bill" (e.g. Tom ran up a huge restaurant bill") must refer to someone physically running upward on a duck's bill, since each word technically permits such a reading. You've got to take into account the construction (e.g. UP is a particle, not a full preposition, when following RUN and has BILL as object). In his response to Jonsson, Jenni said pretty much the same thing regarding lamed ("it can be understood as local or local-directional only in certain adverbial expressions"). In his response to you, he clarified this point again.
(2) Your reference to the "textual tradition beginning with the LXX" again reveals your misperceptions of the matter. The LXX renders the Hebrew l-bbl with dative case. Do you even know what dative case marks?
Dative of Indirect Object ("to, for"): Seventy years to Babylon, Seventy years for Babylon
Dative of Interest ("for the benefit of"): Seventy years for the benefit of Babylon
Dative of Reference ("with respect to"): Seventy years with respect to Babylon, Seventy years pertaining to Babylon
Dative of Sphere ("in the sphere of"): Seventy years in the sphere of Babylon, Seventy years under the purview of Babylon
Dative of Association ("associated with"): Seventy years associated with Babylon
Dative of Cause ("because of"): Seventy years because of Babylon
None of these are a simple local; only a remote locative (e.g. Dative of Sphere) is possible, and most likely we are dealing with a pure dative rather than the more specialized (e.g. context-dependent) local or instrumental dative. The dative case clearly supports Jenni, Jonsson, and the majority of translations....definitely not the NWT.
Also, the context of the specific chapter and the book of Jeremiah supports a locative interpretation.
This has been refuted extensively in the other thread; for instance, your citation of other ch. 29 passages of "in Babylon" in English translation is linguistically silly and is actually evidence against your position (e.g. that lamed is not used to indicate these locatives).