[7" Kindle Fire HD Android Development] mikerackhabit:
Yep, I've got the same issue trying to enable alternate keyboards. Here's the backtrace of the crash that's happening, hopefully it can get fixed soon :)

/AndroidRuntime( 5429): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.settings/com.android.settings.Settings$InputMethodAndLanguageSettingsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.preference.PreferenceCategory.removePreference(android.preference.Preference)' on a null object reference
E/AndroidRuntime( 5429):	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2318)
E/AndroidRuntime( 5429):	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
E/AndroidRuntime( 5429):	at android.app.ActivityThread.access$800(ActivityThread.java:147)
E/AndroidRuntime( 5429):	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1281)
E/AndroidRuntime( 5429):	at android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime( 5429):	at android.os.Looper.loop(Looper.java:135)
E/AndroidRuntime( 5429):	at android.app.ActivityThread.main(ActivityThread.java:5255)
E/AndroidRuntime( 5429):	at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime( 5429):	at java.lang.reflect.Method.invoke(Method.java:372)
E/AndroidRuntime( 5429):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
E/AndroidRuntime( 5429):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
E/AndroidRuntime( 5429): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.preference.PreferenceCategory.removePreference(android.preference.Preference)' on a null object reference
E/AndroidRuntime( 5429):	at com.android.settings.inputmethod.InputMethodAndLanguageSettings.onCreate(InputMethodAndLanguageSettings.java:179)
E/AndroidRuntime( 5429):	at android.app.Fragment.performCreate(Fragment.java:2031)
E/AndroidRuntime( 5429):	at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:863)
E/AndroidRuntime( 5429):	at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
E/AndroidRuntime( 5429):	at android.app.BackStackRecord.run(BackStackRecord.java:833)
E/AndroidRuntime( 5429):	at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
E/AndroidRuntime( 5429):	at android.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:483)
E/AndroidRuntime( 5429):	at com.android.settings.SettingsActivity.switchToFragment(SettingsActivity.java:959)
E/AndroidRuntime( 5429):	at com.android.settings.SettingsActivity.onCreate(SettingsActivity.java:585)
E/AndroidRuntime( 5429):	at android.app.Activity.performCreate(Activity.java:5933)
E/AndroidRuntime( 5429):	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
E/AndroidRuntime( 5429):	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2264)
E/AndroidRuntime( 5429):	... 10 more
W/ActivityManager( 457): Force finishing activity com.android.settings/.Settings$InputMethodAndLanguageSettingsActivity
W/ActivityManager( 457): Force finishing activity com.android.settings/.SubSettings

---------- Post added at 01:15 AM ---------- Previous post was at 12:52 AM ----------

For others running into the keyboard switching issue, you can enable the keyboard via adb:

adb shell ime list -a

This will print out a list of all the keyboards you have installed. For example the default android keyboard looks like:

com.android.inputmethod.latin/.LatinIME:
mId=com.android.inputmethod.latin/.LatinIME mSettingsActivityName=com.android.inputmethod.latin.settings.SettingsActivity
mIsDefaultResId=0x7f070000
Service:
priority=0 preferredOrder=0 match=0x108000 specificIndex=-1 isDefault=false
ServiceInfo:
name=com.android.inputmethod.latin.LatinIME
packageName=com.android.inputmethod.latin
labelRes=0x7f0a003c nonLocalizedLabel=null icon=0x0 banner=0x0
enabled=true exported=true processName=com.android.inputmethod.latin
permission=android.permission.BIND_INPUT_METHOD
flags=0x0

The mId=[id] line is what we care about, in this case the id is: com.android.inputmethod.latin/.LatinIME

Now you can just type:

adb shell ime enable com.android.inputmethod.latin/.LatinIME

but replace the id with the keyboard you want to enable.