You should always encourage all attempts at vocalization that your child makes. Expressive verbal language delays may be due to hearing problems, developmental issues involving the mouth, tongue, palate, or throat, or neurological deficits. While I would never encourage a parent to worry excessively over a "missed" milestone (as they are in reality more flexible than many parents appreciate), if the child in question is being seen for the glue ear problem, you should not refuse any offers of early intervention services, and should consider requesting an evaluation by a pediatric speech therapist if one has not yet been done.
I recommend the following resources to get you started:
Childhood Speech, Language, and Listening Problems, by Patricia McAleer Hamaguchi
The Late Talker: What to Do If Your Child Isn't Talking Yet, by Dr. Marilyn C. Agin, et al.
"Baby Babble", "Baby Babble 2", and "Baby Babble 3" DVDs
The Baby Babble DVDs were created by two speech therapists specializing in very early speech delays. They contain short movies which are amazingly effective in getting young children vocalizing, and each contains helpful tips on remedial strategies as well. For instance, sometimes children are reluctant to make B, P and M noises, which hampers formation of syllables necessary for the first spoken words. Remedial strategies for that problem encourage making noises such as "pop" in response to exciting stimuli (this can be done with toys, not just by using the DVDs). Remedial strategies for vowel sound avoidance can include anything that encourages the child to purse the lips and blow, such as blowing bubbles through a straw.
Advice is consistent throughout all the materials I've seen and read to do whatever possible to encourage all vocalizations-- never correct a child, which risks making him or her feel bad and clam up, though of course having a conversation where one models words in different forms is to be encouraged. Researchers also do tend to encourage babbling back at a child who's not ready to form words yet. In general, do anything to make vocalization fun and stress-free, and increase mobilization of the tongue, mouth and throat. On the DVDs recommended above, you will see the therapists act extremely overjoyed at every sound the children struggle to make. You will also notice them using exaggerated facial expressions when making sounds in front of the children, as one area that may be lacking is understanding / modeling of the correct movements of the mouth to make a certain sound.
Early hearing problems, even ones falling short of deafness, should be addressed as quickly as possible. Not only do they impact early language development, but even problems resolved with tubes and the like, which disappear as a child gets older, have been linked to attention and language processing disorders.