Spanish does not have a lisp. During the medieval age, in the territory that would be called Spain in the future, there were several dialects (or "norms") of Spanish. One of them pushed for seseo (no /θ/, "th" as in think) and other for a combined approach. The latter was chosen by a king (Alfonso X the wise), and the rest is history.
However, all dialectal varieties are accepted by the RAE (Royal Academy of Spanish) jointly with the Spanish Academies of the American Continent regulates the language (like the Académie française for the French language).
So, in Seville (Spain) most people does not use the /θ/ sound, as in Venezuela, for example.
To sum up, please stop saying "Spanish has a lisp" because it has the same "lisp" than English or other languages with the sound /θ/.
Spanish is considered a "Romance" language, along with French, Italian int al. English is considered a "Germanic" language along with German, Dutch int al. English alone has at least three major periodic based "versions" - Old, Middle, Modern. There were also events such as a major vowel change where the way we pronounce vowels today differs from before that event.
Spanish seems to have a famed "lisp". However that simplistic approach to a complex language and Spain as a whole ignores rather a lot of history, culture and is frankly an insult! As we say in Britain - "Viva la difference".
English as spoken in Britain and elsewhere should borrow and bother from every language it ever trips over. It should always evolve and mutate and continue to become ever more flexible. It should also continue to enable useful "pidgins" which are amalgams of English bolted on the side of another language and vice versa.
What English seems to have lost compared to the other Germanics is a lot of formal complicated verb conjugations and nounal declensions and noun genders and quite a lot more. Complexity can be bolted on but it is optional. Subject object verb is also quite fluid too in English. I believe German at least insists on a verb dump at the end of a sentence. English still has many of these structures - active, passive, subjunctive verbs (transitive, intrans etc); Nom, Voc, Acc, Gen, Dat, Abl for your nouns but they are largely implied via other words instead of suffixes.
English is quite literally and vocally French!
(lingua franca - language of the Franks)