## Description:
Languagetool GUI is crashing if I choose "en_US" regardless of the entered text. Other languages are working fine.

## Additional info:

```
Name : languagetool
Version : 4.0-1
Architecture : any
Depends On : java-runtime-headless>=8
Optional Deps : java-runtime: needed for the GUI version [installed]
libxtst: needed for the GUI version [installed]
gtk2: needed for the GUI version [installed]
Build Date : Wed Jan 31 12:26:44 2018
Install Date : Wed Feb 7 16:13:25 2018
```

```
java -version
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on
openjdk version "1.8.0_162"
OpenJDK Runtime Environment (build 1.8.0_162-b12)
OpenJDK 64-Bit Server VM (build 25.162-b12, mixed mode)
```

## console output:

```
java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: Could not check sentence (language: English (US)): 'This is a example input to to show you how LanguageTool works.'
at org.languagetool.MultiThreadedJLanguageTool.performCheck(MultiThreadedJLanguageTool.java:195)
at org.languagetool.JLanguageTool.check(JLanguageTool.java:580)
at org.languagetool.JLanguageTool.check(JLanguageTool.java:555)
at org.languagetool.JLanguageTool.check(JLanguageTool.java:512)
at org.languagetool.JLanguageTool.check(JLanguageTool.java:495)
at org.languagetool.gui.LanguageToolSupport.checkText(LanguageToolSupport.java:742)
at org.languagetool.gui.LanguageToolSupport.access$1700(LanguageToolSupport.java:55)
at org.languagetool.gui.LanguageToolSupport$RunnableImpl.run(LanguageToolSupport.java:908)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.util.concurrent.ExecutionException: java.lang.RuntimeException: Could not check sentence (language: English (US)): 'This is a example input to to show you how LanguageTool works.'
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at org.languagetool.MultiThreadedJLanguageTool.performCheck(MultiThreadedJLanguageTool.java:192)
... 14 more
Caused by: java.lang.RuntimeException: Could not check sentence (language: English (US)): 'This is a example input to to show you how LanguageTool works.'
at org.languagetool.JLanguageTool$TextCheckCallable.getOtherRuleMatches(JLanguageTool.java:1119)
at org.languagetool.JLanguageTool$TextCheckCallable.call(JLanguageTool.java:1022)
at org.languagetool.JLanguageTool$TextCheckCallable.call(JLanguageTool.java:989)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
... 3 more
Caused by: java.lang.RuntimeException: Could not connect OpenNMT server at http://127.0.0.1:7784/translator/translate
at org.languagetool.rules.OpenNMTRule.postToServer(OpenNMTRule.java:194)
at org.languagetool.rules.OpenNMTRule.match(OpenNMTRule.java:83)
at org.languagetool.JLanguageTool.checkAnalyzedSentence(JLanguageTool.java:667)
at org.languagetool.JLanguageTool$TextCheckCallable.getOtherRuleMatches(JLanguageTool.java:1077)
... 6 more
```




## Steps to reproduce:

* start languagetool
* choose language "en_US"