I feel for you. I understand why other people are saying that this can be a blessing, but I think it is ultimately due to your OCD. Some people with OCD say things compulsively, and I guess being afraid to talk has its advantages compared to that, haha! But the mere fact that being slow to speak can have its own advantages does not mean that it is not creating problems for you. Hopefully, this tendency can become an advantage (if you can learn to be deliberate about what you say without being paralyzed by fear), but don't let that fact make you feel like your suffering is not valid, or that it's not OCD.
This is definitely a huge problem for many people with OCD. They are afraid of what they might say or do. The best advice I can give is to know that these thoughts come from your brain. You don't have to act on them. There is a major disconnect between your thoughts and your actions, and although it is harder to control our speech, it is still true that just because you think things, it does not mean that you will say them. Have you ever been on a really high place and gotten an inexplicable urge to jump? Or been driving and suddenly out of the blue you imagine swerving into the opposite lane? Most people have. It doesn't mean you actually want to do those things; much less that you would ever act on those impulses.
I've had these types of fears too (though not nearly as bad as you seem to be having them). In my experience, you only really get over them when you realize that you are not obligated to act on your thoughts. When you have a bad or blasphemous thought, remind yourself, "I have control over myself. I can't control when these thoughts come, but I can control whether I act on them, whether I dwell on them, and how much I let them worry me". Ultimately, you have to trust in yourself; to know that you have control over the things you say (I know, easier said than done). But more importantly, you have to trust in God. Know that God will protect you and keep you from committing sins if you submit to him. And if you do slip up and say something, he will forgive you if you repent. Take comfort in verses like 1 Corinthians 10:13 ("No temptation has overtaken you except what is common to mankind. And God is faithful; he will not let you be tempted beyond what you can bear. But when you are tempted, he will also provide a way out so that you can endure it."), Psalm 34:19 ("The righteous person may have many troubles, but the Lord delivers him from them all"), 1 Thessalonians 5:23-24 ("May God himself, the God of peace, strengthen you through and through. May your whole spirit, soul and body be kept blameless for the coming of our Lord Jesus Christ. The one who calls you is faithful, and he will do it."), Psalm 121:3 ("He will not let your foot slip -- he who watches over you will not slumber"). I also find Psalm 23 and Psalm 103 comforting.
It is important to face these fears head on in a constructive manner. Try to address your fear of speaking in small increments. Read the Word as much as possible, and try to apply it when you speak. Death and life are in the power of the tongue, so try to speak life. Proverbs 12:25 says, "Anxiety in a man's heart weighs him down, but a good word makes him glad". I believe that saying good things and using your words to bless others and reaffirm your beliefs can actually relieve some of your anxiety. Look for opportunities to help people by speaking. Perhaps share encouraging verses, ask people about their interests, or give compliments. Pray from Psalm 19:14, Psalm 141:3, and Ephesians 4:15. Pray that God will help keep you from sinning in speech, and forgive you when you slip up. And above all, remember, it's not you; it's OCD!
Sorry for the super long answer, haha. BTW, your English is fine; I understand you perfectly well.
