The English language is reported to have as many as 500,000 words based on major publicised dictionaries. If various technical words are included the number grows to 1,500,000 words. With the growth of the Internet the number of words that are being coined and used is growing everyday. So the day when we literally run out words to describe things will arrive.
Although the debate over the longest English word still continues, we could probably say that words longer 20 letters are difficult to use in normal speech. Considering the words to be maximum of 20 characters long a total of 26 to the power of 20 words can be made. (26 to the power of 20 = 1.99281489 × 10 to the power of 28. So we have more than enough words in English Language to last a few centuries?? Or will we out grow this number by discovering or inventing those many new things to describe? Time will tell if we Will have to add more characters to the English Language.
Probably we will resort to using numbers along with the alphabets before actually going on to create new alphabets. So a word like "10potato" might mean an actual word that has no connection whatsoever to a potato as we know it today.
Linguists may argue that humans would rather add few more alphabets to a language than use such long words. However, based on the way the lanuage is going to be used in the future, we may not add more alphabets but actually use long words which are cross-referenced in huge online dictionaries.